Okay, I'm throwing my .02 into the mix.
I have a pair of SongTowers that I've run with a few different set-ups.
First was a AVA Insight Amp/T8 pre/Insight DAC combo. This was a very nice sounding set-up but I found it very forward and I experienced listener fatigue after approx. 20 min. There was a harshness to the treble that just did a number on my ears.
I bought a Vista Audio i34 next. I really enjoyed the smoothness of this little integrated. Great imaging and fullness without the harshness. What I missed was the authority in which the AVA gear just brought the bottom end out. I still own this amp and will probably use it for a second system sometime in the future.
I'm now running a Wyred ST500 Amp/DAC 2 combo. This set-up gives me the tube-like sound of the i34 (yes, I was surprised of this too!) with the nice tight, authoritative bottom end. It drives the SongTowers with ease, and really makes them sing. I'll be keeping this system together for a long time.
I was very apprehensive about going class D, but now I'm glad I made the switch!
Very interesting, baumer. I also auditioned* an AVA pre-amp and amp combination (AvaStar and FetValve Ultra+ 550 with double die option), and I also found them very forward, with an upper mid-range emphasis that kept causing me to turn the volume down. The amp also had a slight buzz in the transformer (AVA said it wouldn't affect the sound, suspected that it was due to some DC on my A/C line, and was willing to replace it if I had kept the amp).
In any event, I returned them and got the Wyred4Sound SX-1000 monoblocks and STP-SE preamp: no fatigue, no upper midrange emphasis, no loss of detail or bass or anything else. Just terrific music (and a much more convenient pre-amp that lets me switch sources with the remote and adjust phase on the fly).
*By auditioned I mean that I bought them and had them in my system for a couple of weeks and returned them under the AVA 30-day money back guarantee. The glare that I heard in the upper midrange drove me to surround the speakers with sound panels. That did not solve the problem, but I kept the panels anyway, and it sure made the Wyred4Sound setup sound good.