I can't speak about the NFB-6 as I haven't heard it but based on what I've read of your reviews, you may actually like the SA-31. It's sound signature is likely closer to the V200 than the NFB-6. It uses a completely different topology and traditional through hole components vs SMD parts. The topology is supposedly modeled after a mid 90's Accuphase amplifier. Similar to how the V200 is based on an old Nakamichi circuit.
It's interesting how some manufacturers are looking back to older Japanese stereo equipment as inspiration for newer products. Also, The SA-31 is single ended only and so is optimized as such. I'm really curious to hear the Soloist. I can't say for sure since I haven't heard the Soloist, but I would imagine the SA-31 is closer in performance to the Soloist than the NFB-6. I feel it's a very special amp in the otherwise somewhat generic Audio-GD lineup.
To stay on topic, It's also had good impressions from Hifiman owners as well, HE-400, HE-500, and HE-6. At about $550 shipped, it's an excellent alternative to something like the Lyr, and I personally greatly prefer it over the Lyr I owned.