Summary:
Currently, I am unable to split the two systems (music/HT), so the amp has to be capable of both. Here's the current rig- Lexicon DC-1 v2.01, Rega Planet CD, Snell E.5 (90dB, 4 Ohm) towers.

First, the contenders:
Krell KAV-250, $3300, marked down to $2800
Anthem Amp-1 (tube), $1299, marked down to $744 (!)
McIntosh MC352, $7000 (used for reference)
Atma-Sphere MA-1 Mk1 (tube), $6000, used $3000

The setup(s):
The first setup was the Atma-sphere amp with the Atma-Sphere MP-1 tube pre and a Sony SACD player through Vandersteen 3A's. The Vandy's were well out in the room- over 6 feet from the front and 4 feet from the sides, approx 6 feet apart. I was around 7 feet from the speakers, 5 feet from the back wall. The room was heavly modified with traps and panels.

The second room was all the other amps through a Mac MX332, Mac MCD7010 CDP and B&W 803's. These guys were about 10" from the back wall and offcenter in the room by about 3 feet with the right speaker only 2 feet from the wall and 6 feet apart. I was around 7 feet from the speakers. It was fairly bare, with another 802 setup opposite, behind me.

The review material:
Radiohead, OK Computer, "Exit music (for a film)" and "Lucky"
Braveheart Soundtrack, "Betrayal and Desolation"
Pink Floyd, DSOM, "Speak to me/Breathe" and "Us and Them"

The reviews:
The Atma-sphere's were first. PF's "Breathe in the Air" was absolutely mesmerizing. Oh. My. GAWD. It's like somebody plopped Waters' head about 3 feet behind the speakers, right smack in the middle and he was singing right at me. Un-freaking-believeable. I was like a little kid again. Smile all the way across my face. It sounded THAT good. Unfortunately, the more I listened, the worse it seemed to sound. "Us and Them" lacked the impact I was used to. To put it bluntly, there was zero Bass. None, zip, nada. Moving the chair around helped, but it was still anemic at best. Hmm- the only thing I can come up with is that maybe the room was overdampened or the speakers were too far out into the room. The speakers got good reviews in Stereophile... Radiohead's "Exit music" was stunning until bass was asked for, and "Lucky" again lacked bass when called for. Hmm. But the midrange! Vocals were simply STELLAR. I can't beleive how realistic it sounded! My first "You are there experience", and it boggled the mind. The braveheart track was simply pathetic without bass- I purposely picked this track because of it's huge transitions- from bass drums, timpani's (sp?), and horns to violens, it's got enormous fluctuations. It sounded quite flat.

The Anthem came next at a different store. Immediately, slightly more forward sounding than the Atma's, it also completely failed to present that "you are there" impression. However, bass was nice and tight and quite abundant. Well, so much for that "Tube amps lack bass" arguement. This one poured it all out for me, though without the liquid midrange and holographic imaging that the Atma's presented.
Switched over to the Mac, just for kicks to see what I was missing. Much darker- almost intriguing and seductive. The soundstage was narrower and still lacked the depth of the Atma's. However, I found that it was perhaps a little too flat for me- not lively, not involving, but still VERY nice sounding. I liked the Anthem better, I think. However, take note: The anthem was turned up more than the Mac (unknown to me, of course..) I couldn't help but think of Eyespy's DBT testing: "The louder one will sound better". Ugh.

Enter the Krell. Pink Floyd, "Us and Them". This amp was much brighter than the Mac, with more depth and a wider soundstage. It lacked the bass control of the Mac. Again, the volume control had been turned up (damn that salesman), but only slightly. I fixed that and played the Braveheart track again. Drums had authority, but throughout the passage, a french horn blasts along, either irritatingly or beautifully. This was irritating. I found that I wanted to turn the volume down. I think the Mac won... Otherwise, it had presence and a nice wide stage, if still not very deep.
Return of the Anthem. Gone was the irritating French horn, replaced by a midly annoying horn, but with much more layering underneath. I could make out the details of the rest of the orchestra previously muddled up by the Krell. Overall, I like the Mac, but for $7000, there's no way.

I finally brought the Atma-Sphere's home for a demo on my own gear and what a difference it made. The bass had authoity (almost frighteningly so) and the soundstage was still terrifyingly real. I really don't have any words to describe it except perhaps "magical". I don't know why I even considered anything else nor why I hadn't made this purchase earlier. If I'd only known what I was missing! Simply put- this amp will never leave my listening room. I can see myself upgrading every component in my system except this one.... Trully a remarkable amplifier. If you have the means and the urge- you owe it to yourself to listen to this amplifier.

The bad's (and every piece out there has them): it runs hot as all hell. You can turn the heat off in your listening room 'cause you won't need it. Also, it draws obscene amounts of power (~500W each) so your electric bill will be adjusted accordingly. Finally, biasing is not as easy as some newer amps in that you have to switch the "+" speaker cable to the "bias" terminal to bias it; then move it back to listen. Just a slight hassle.

Overall, this amp rightly deserves 5 stars since it is by far the best amplifier I've ever heard.

Strengths:
Exceptional soundstage, tons of power

Weaknesses:
VERY hot, large

Similar Products Used:
Krell KAV 250, MacIntosh MC352, McCormack 225, Anthem AMP1, Proceed HPA 2, Levinson 332,

Summary:
I am fortunate to have been exposed to some incredible amplifiers. These monoblocks, in my opinion, provide the most musically accurate sound amplification available. Period.

On a pair of full-range electrostats, these 140 watt "rated" monoblocks will out-perform 1000 watt rated solid state amplifiers! So powerful is the bass, that on some recordings, the staters on my Sound Labs actually rattled - something I have never encountered before!

I am also fortunate to have the highly-rated solid state Pass Labs X-600 monoblocks. In comparison, the MA-1's have just slightly better detail and better bass, while the Pass Lab amps run much cooler but are heavier. The MA-1's bass is even better than Krell, which are also excellent amplifiers. The MA-1's sleek, industrial design and meter is consistant with the handsome Pass Labs X-series amps. However, there is no "cool" blue light - sorry!

In any case, the sound these amps produce is almost frighteningly real - clean, open, "air", wide soundstage, unbelievable detail - it's all there and then some. And, don't let "tube terrors" get the most of you; there is no "warmth" or other tube-related anomalies - just clean, accurate musical amplification.

From a technical standpoint, consider this: There is NO output transformer, NO overall feedback (read: stable!), class A design, no expensive or rare or matched output tubes required, simple and reliable design, no biasing every output tube (one bias for the entire output), are relatively light (about 40 lbs), are relatively speaker load independent, and they run quiet. They do run hot (class A), so you may need alternate cooling for small audio rooms. The Atma-Sphere factory service is also outstanding, as is the build quality.

The MA-1 sounds great on a variety of speakers, but you really have to hear them on full-range electrostats. There is a saying that "you can have your cake and eat it". With this combination, you get the "whole cake factory!"

Even if you don't plan to buy, make sure you listen to these remarkable amps from Atma-Sphere.

Other components: Pass Labs X-600 solid state amps, Krell MD-2 CD transport, Meridian 563 DAC, Sonic Frontiers Line 1 preamp, PAD Collossus speaker cables, Sound Lab Aura speakers.

Strengths:
Clean, Open, Musically Accurate, probably The Best Amplification Available.

Weaknesses:
They run very hot

Similar Products Used:
Krell KSA-300S, Pass Labs X-600

Summary:
A friend of mine ownes the ma2 amplifier which was my intro to Atmasphere electronics. I almost immediately sold my other amps to make the purchase of the Ma1-mk2 less painful.
There may not be anything out there that controls a speaker the way these amps do, and with openness and detail that must be heard to be appreciated. I use Sound Lab electrostats that like a lot of current, and these amps deliver the goods. These amps have also been used on Green Mountain audio "Imago" speakers, with phenomenal results.I understand why Atmasphere amps are seldom replaced.
Buy them.

Strengths:
unsurpassed speaker control / incredibly open/detailed sound

Weaknesses:
none

Similar Products Used:
years of tube & solid state