Even with 250 ohm beyerdynamic dt-880 pro there is ample volume on a pc that normally only gives these cans low volume.

Full volume gives no distortion percieved at all.
The tight deep base remained on the dt-880s but seemed to get better
when xm4 volume was at 3/4 up and player output volume lower!
Bass boost was not boomy but wasnt needed and bass weak cans like
my Grado 80 benifit greatly with that feature,seems to me the 6db gain is exactly as claimed!
Small size is pocket perfect!
battery meter reads on startup and easily understood!
Crossfeed function works ok but i liked the stereo default as it came!
Quality crafted,design and optional functions are well thought out!
Screws are strip proof ,due to case design,well thought out again!

Factory tested and setup per buyer option.
Quite user friendly.
Very smooth volume transit up and down,with no noise!
Blue led not a brite nusuance, but flashlit mode amber light could be a life saver in darkness finding keys ect:
Sound quality is a bit better all around especially in the basement !

Im not sure unless you could compare a few different amps but as i said at this price point i didnt see much compared to the xm4.

Overall its a good home, portable pocket amp, and cmoy amps dont compare and i didnt see any products with a lower price that came close at all,however a little more money you can get a little better amp,on up too tube burning $2500.00 if you want,and i guess electro static headphones if you want too pay the ransom demands!
I JUST NEEDED A LITTLE MORE VOLTAGE for 250 ohm headphones ,too feed the bass requirement ,and the grado 80s have a serious bass deficit going on ,not the dt-880 pro models though,but it did get a little stronger and still really tight bass resolution too!
After hearing a standup bass recording sound better than i could have ever imagined, i wanted to make sure i had enough voltage leftover too resolve complex deep bass passages!
At this time i couldnt spend any more than this.
I am pleased with this little xm4,its packs alot in a small package!

Customer Service

30 day money back of course!
practical devices focas on only a few products!
There main concern should be not using united states postal service because
any of there shipping adds days to delivery most times.
I didnt see an optional delivery such as ups but the usps caravan did break through the sand storm and get here!
Happy in Virginia !!!

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Ive never had a headphone amp before,but i needed one and need not worry about high ohm cans now!