Out of curiosity, why did you pick the Soloist vs the Soloist SL? I debated between both and decided the SL made more sense for the TH900 since it doesn't need a ton power and I personally prefer analog volume. Haven't gotten it yet, so can't say how it sounds, but hoping its as good.
I had the same mindset as you initially. I reached out to Drew at Moon Audio and he said the Soloist produces a much more refined sound compared to the SL and that Stepped attenuators are always a better sound. As the signal only travels through 1 resistor. Verse with wiper control the signal is more saturated. For those two reasons I figured spending a few more bucks was worth it. Very happy I did.