[amb]

 
Quote:

Might want to note that the M^3 does have some dependency on quality of power supply, don't expect to throw in a cheap switching supply and expect it to work wonders.

Actually, very-high PSRR is one of M³'s strong suits.  It's an IC opamp-based amp, and most opamps have high PSRR.  The capacitance multipliers in M³'s supply rails increase the PSRR quite a bit further.
 
This is of course, not to say that a good quality power supply is unnecessary.  A good linear supply like a σ11 provides many benefits beyond just low ripple and noise.

 

[sr20dem0n]

I do own both of these amps (HA-171 and M^3).  Unfortunately, I use them in different locations (home vs work) with different sources (E-MU 0404 with dedicated DAC vs iPhone) and completely different headphones (HD595 vs Ety ER4P), so I can't really compare them.
 
They both sound great though, I don't think you can go wrong either way.  I did use the M^3 with my HD595 briefly when I was first testing it out, and from what I recall it did sound a bit better than the HA-171, but without a longer A/B test I wouldn't be able to really put my finger on it.  The price is completely different though...HA-171 is about $400 to your door ready to go, M^3 was over $450 in parts alone, plus hours of measuring, soldering, cleaning, testing, and a TON of measuring, drilling, filing, etc.  Not to mention if you get some bad parts, or screw up during your measuring and blow a part or two, or if you screw up in your case modifications and have to buy a new one or at least new panels, etc.
 
I'm not saying the M^3 is a bad idea, far from it, in fact it's a fun project, but a $400 OTS product shipped to your door ready to go, and a $450+ collection of random parts that you have to assemble, mount, test, and debug yourself isn't really a fair comparison.