It’s been a long time, but for those interested...
I went from the tubes, which were completely inappropriate for these speakers to..,.
1. Pass Labs X260.8. These were a big improvement, but the bass was still muddy.
2. Classe Delta Monos. These were another step up. Bass was quite good, but the highs were harsh and shouty.
3. NAD M27s. I have a pair of these for the home theatre. Tried them out as monos and they sounded better than anything prior. Bass is stunningly good, but the highs lacked a lot. Very dry sounding.
4. Boulder 2150s. Just got these and there is no contest with anything prior. Incredible bass, beautiful mids and highs. The tweeters have never sounded this sweet and extended before. Obviously, way more expensive than any of the others. What a rabbit hole...
My local dealer, 3mA Audio in Houston handled the setup and install. Spectacular job. They recorded a lot of it for YouTube. Check out Audiophile Junkie on YouTube.