Mariusz, I'm sorry I was out today, and missed your post until now. But, thank you very much for the invite, it would have been really special to be there with you guys. 3 guys getting together is basically an audio club, isn't it?
I did a review here on Audiogon on the Granite 860.1 monoblocks that I owned. I was going to do one on the 657 as well, but didn't get around to it. I've always felt as you described, at a loss to define why Granite isn't more well known in the audiophile circles. A lot of people complain they cannot find a good made in the USA high-end audio brand offering good value, but that point seems difficult to justify to me with the likes of Cary, Manley, Quicksilver, Rogue, etc., and to that list I will add Granite.
The one word that would describe my overall impression about Don's designs is musical. He has the unique ability to skirt that hard to draw line between clinical sound and caramel colored euphony. A few years ago, when I first got the monoblocks, I'd been fighting a brightness problem in my smaller room, and had changed out every other component in the system. The monoblocks allowed me to finally overcome that, and sit down and enjoy the music. Later, the issue was straightened out by addressing the room, but I think that comment I just made speaks volumes about my experience with Granite products.
The 657 is a unique product in that it offers both solid state (fixed) and tube (variable) outputs, and each offers quite a different sonic presentation, while still maintaining that musicality I spoke of. The solid state is richer, more laid back, and offers much better low frequency performance. The tube output is more detailed and engaging, with a nice rosiness that tubes add in the best of circumstances. I'll probably sell the 657 soon, as I'm awash in CD players, and don't get much use out of it these days.
Reliability of both products was perfect. I had one issue with the monoblocks that was giving me a bit of a headache, but after speaking with Don, he instructed me on what it actually was (no problem with the amps), how to fix it, and within about 2 minutes of doing the procedure he laid to me, everything was perfect.
Don is a very upstanding person to work with. He cares about making his customers happy, and actively works at helping people get the most they can out of the products.