I finally read Mike Fremer's review of the 2150s. It reads very like the review of the Boulder 2060 in www.positive-feedback/Issue27/2060_boulder.htm some years ago. I agree with his review of the 2150s but he does, IMHO, make one error. He writes at the very end of the review: "You can't have everything." Actually, you can.
The reason I did not buy a 2160 (the stereo version of the 2150s) is that it was only a little better than my 2060 and I had already heard the 3050s at the Boulder factory. The 3050s get it all - the Tone Audio review is right. I expected the 3060 (the stereo version of the 3050s) to also get it all -- and it does. My audio friends who complained that the 2060 wasn't quite "musical" enough were floored by the 3060.
would love to hear the big 3060 someday. I was very impressed by the 2060 back in the day, and still consider it a fantastic amp in the grand scheme of things. But i also believe the ante has been massively up'd by a number of designers, and that certainly includes Boulder by all accounts i have read. Congrats and enjoy.
You now have a fellow XLF owner in Microstrip, and now that he is 'assembling' a system around it (Vivaldi full stack is his original digital which i have to imagine will remain)...it will be interesting to see how he builds it.