I was looking for a step up from PA2V2, admirable though it is and fond though I am of it. I listened to a friend's Headroom Maxed Out Home Amp that showed what I was missing because of the PA2V2.
 
I got this m901 used. I generally feed unbalanced analog sources and am happy that I can distinguish between my various disc spinners.
 
Using the coaxial digital input from a Sony DVP S7000, I was not able to tell the difference between the inbuilt DAC and the Sony's analog outputs. No mods to either. Headphone was a Focal Spirit Pro.

An interesting introduction for me to tube sound. No idea if this is a faithful representation of the genre.
 
When I turned it on it the first time, left channel had lots of hiss. But the signal was equal in both channels, when playing music. So I decided to keep it for a while. After a few hours, the hiss evened out, but still was noticeable with the following equipment. Hiss was with only the headphones connected to the amp, no sources or cables.
 
 
The nominal impedance of HD 280 and HTF 600 are 64 and 56 Ohms respectively. The hiss though lower than in the others, is still clearly audible to me, especially in quiet passages of classical music.
 
When I contacted Schiit service, I was told this is working as designed and that some level of hiss is normal for tube equipment with these headphones. Again, I have no way of comparing this to any other tube equipment.
 
I still kept it because I was going to use this in a noisy work environ. And it was fun to listen to. And they got a few points for a funny user manual.
To me, this is unacceptable if used in a quiet listening area.
 
After a couple of months of using a few hours a week on average, the hiss seems to be worsening. Chain: computer -> USB -> micromega mydac -> HD 280. I'll wait a little more and if this trend continues, hopefully send it in for some service.
 
The other amps I have are the PA2V2 and a Grace m901.
My rankings in ascending order: PA2V2, Vali, m901.
The Grace seems the most neutral of the three to my ears.
 
If I had to pick a genre that this excels for me: Jazz and Blues.

I am happy with this DAC.   . Instruments sound good. There is a smoothness to the sound that makes me smile.
 
This was a demo unit, hence the lower price. But the corners of the plastic box do not close completely. So light leaks out, which though non-functional looks funny in the dark of a recessed space. Tape you say? Perhaps. 
 
Equipment:
Squeezebox touch USB -> Micromega mydac -> PA2V2 -> grado sr 60