I'm going to replace my Dali 104's with a new speaker, so I've auditioned (amongst others) the B&W DM 603. Here's my impression:
* Bass
Articulate and tight, but speakers needs to be placed away from rear walls.
Needs a tight and controlled amp to avoid a boom-boom sound. Goes deep and dances away well with the right equipment. A bit warm, doesn't suit hard rock nor super charged techno.

* Midrange
Sweet and detailed.

* Treble
Detailed, airy but a touch forward.

* Overall sound
Very good, especially for pop/rock, new age instrumental and soul. Vocals
sounds good. Good soundstage. Needs to be biwired to give it's best.

I like it, but I won't buy it (I need something that can be placed quite close to a rear wall).

I accidentally posted this in the wrong place. I'll try again
These kick arse for the cash. I picked mine up in September for a cool $850 (Generally $1000/pr). I'm running them with Transparent "The Wave" cables and the sound is phenomenal. Go to your favorite Hi-Fi store, throw in a copy of Hemispheres (Rush), and hear what an awesome pair of floor speakers with a passive radiator should sound like.

These kick arse for the cash. I picked mine up in September for a cool $850 (Generally $1000/pr). I'm running them with Transparent "The Wave" cables and the sound is phenomenal. Go to your favorite Hi-Fi store, throw in a copy of Hemispheres (Rush), and hear what an awesome pair of floor speakers with a passive radiator should sound like.

After listening to these speakers twice, and having the same impressions, I am not impressed.They have a muddy sound, not very detailed. While the sound is full-range, there is just enough detail. The JM Labs models for the same price are a lot better.
The 604 sounded a lot better - more authority, more detail. Very large difference.

The B&W DM603s are at a price where they will get plenty of competition. The PSB Stratus Bronze, KEF Q35, Energy C-4 and C-6, and Paradigm Ref. Studio 60 are excellent speakers in the 603s price range. However, in my opinion, the 603s come out closer to the top:
Stratus Bronzes are somewhat cold-sounding, but very smooth.
KEF Q35s have excellent transparency but lack authority.
Energy has thunderous dynamics but subtlelity was lost past the little C-2.
Paradigms are somewhat bright and brittle but have excellent soundstage depth.

The B&W 603s do have flaws - their "rounded" bass sound lacks acoustic "grip" giving the bass a flubby, loose character. However, their midrange and treble is
top notch and very defined. They tend to sound more like the Paradigms in terms of brightness. The midrange does shine vividly, though. Foam bass-port plugs are supplied to modify bass alignment to your taste. When used with NAD, the balance is a little thin but the clarity is breathtaking.

A "four" rating for overall performance vs price.
A "five" for midrange quality vs price.

When I heard this speaker for the first time, I really thought they were great! Smooth with a lot of bass... However, this was about three years ago and my listening capabilities have improved since then. Today I find it detailed and it has a great midrange. But! Bass is far too wolly and undefined. In Sweden a pair cost £400 and they may be worth it, but I would rather go for Dali or Acoustic Energy in that price range.
B&W is still my speakerbrand of choice, but the 603 is hopelessly out of date.

In trying do buy a descent stereo system on a budget. I started looking at three speakers in the $1000 price range. The B&W DM603, a Def tech model (sorry I don't recall the number but it listed at $1000), and a NHT super two (now this lists at $750 but this was the proce range). Right off the bat I eliminated the Def tech model because it was really quite boomy in the bass. Though it did project sound quite nicely. Then the battle came between the B&W and the NHT. Sure the B&W had an advantage on price but that is not always the deciding factor. Of course for this it was. THe B&W sound was warm and inviting and as far as I could tell was not missing a lot of low end. The NHT was very harsh and in your face. As vocals seemed to have a wispy quaility to them. Definitely the B&W was the best. I am currently using this system at home with a Rotel RA-971 integrated amp and a RCD-951 CD player.

I purchased these speakers 10 days ago as an upgrade from the B&W DM305 speaker. Definitely better imaging and detail but with a mid-bass hump that colored the sound from smoothly transitioning to my Velodyne HGS-12 subwoofer. I returned them to my dealer and purchased the B&W CDM7SE. Now I have found audio heaven!! Even better imaging and detail with a smooth transition to my subwoofer.

I am very disturbed by the reviewer below. "never put a passive radiator and a port in the same box?" What the #)$# are you saying??? You have no damn clue about box design, and I personally know becuase I design my own speakers. disguised as a woofer? B&W put the passive in there for a reason.. it's extremely efficient.. But you wouldn't know that, would you? The speaker was not intended to shake the walls. That is why they make the ASW series. You aren't even decent enough to leave your Email address. You make me sick.. Go back to your optimus and bose speakers and shut up.. I bet you like those 901 bose too huh?

Absolutely right....For those who are looking for boomy / disco atmosphere music, that is not the best choice...but for the others who are expecting warm and natural sound it is perfect choice...
B&W engineers know what they are doing...you will not be fooled !
Great speakers.