I've basically finished the max aside from cleaning up the wiring, and have put it through its paces with my Audio Technica ATH-AD900 on my old Sony DVD player (will hook it up to a better source very soon). Here are my thoughts......
My first set of tubes were some 12FK6, burnt in for about 8 hours. I agree that the 12FK6 tubes sound nice and airy. I agree that they lack bass and punch. I'll try my other set of 12FK6 later today.
The 12AE6A have been in for about 5 hours and I'm listening to them now. They get back a lot of punch but are slightly veiled compared to the 12FK6 - though this has improved since the tubes first went in, so maybe the tubes need more time. Even so, I think I prefer these to the 12FK6.
Comparing the 12AE6A Max to my M^3 (OPA627BP in L/R, AD8610 in GND, variable gain 2-12) is interesting. The Max is ever so slightly warmer and smoother, with the M^3 being more neutral and detailed (I get even more detail out of the M^3 with AD8610 all round). Treble is good on both, and both are sibilant on music that I know to be sibilant; the M^3 moreso, which I take as the M^3 having slightly better treble extension than the 12AE6A tubes (but this could still be a detail thing). Soundstage is excellent on both, with the M^3 having a tiny bit more front/back depth.
Both amps are capable of driving my KSC-75 as mini speakers (the poor little buggers!) to ridiculous volume levels. No lack of power in either amp. But the most interesting thing in my comparison is that the M^3 maintains more of its punch at very low volume levels (even at a gain of only 2), whereas the Max needs a little bit more volume before things really get rocking. I really think the tubes like to be worked hard, whereas the OPAMPs are less picky.
Lastly, the Max is definitely sexier - I can understand the emotive draw of tubes! The PCB symmetry is nice and all the big caps look very imposing. The M^3 is more understated and clinical looking.
So that's my $0.02. At the end of the day, I am VERY happy with the Max, considering it cost half what the M^3 and S11 combo cost me. It will probably serve duty on the Rec monitor of my HT amp, for mixed TV, DVD and Xbox360 usage while the M^3 will specifically do CD duties. And I'm *definitely* selling my Corda Arietta!
[EDIT] Just thought I'd add specs for key positions at this point....
CR1 - 4x 1000µF Nichicon UPW
CA4/5 - 4x1800µF Nichicon UPW
CA2 - 1000µF Nichicon Muse ES
CA7 - 470µF Nichicon Muse ES
CA3/6/9 - 0.22µF Wima MKP10
CA8 - 0.18µF Sprague Vitamin Q
QB8/9 - 2SC3422/2SA1359
RB14 - 10ohm KOA
PS set at 27V
Tube bias set at 13.5V (hot)
DB bias at 110-115mV, and within 1mV B1-B2
DC offset <1mV
