i heard the Boulder at a dealer a few times and wasn't impressed (it seemed grainy and dark).....but i would add that i never cared for the overall system it was in...Wisdom speakers that were never properly dialed in....they couldn't figure out the Wisdom "brain" properly.....so discount my comments accordingly. i have been told by people i respect that Boulder amps are very special. and i would point out that i have been told that the Boulder is grain-free and very open in contrast with my own observations.
my 2 favorite solid-state amps are the Halcro and the Edge.
i had the Halcro DM-58 in my system for 3 days last year and it is very special....the fastest, most transparent, most detailed amp i have heard.....but.....it may be too lean sounding for some systems/speakers. i heard both the Halcro and the Edge amps at CES and there i preferred the Edge ($30k monoblocks)....it was mated to the Lumin White (sp?) speakers. easily the most "musical" and "edge-less" solid state amps i have heard.
i would guess these 3 solid state amps are all winners in the "right" system (if you want a ss amp ;^)
i would choose the Edge, then Halcro, and then the Boulder based on my experiences and listening preferences.