Update:
In my case the pre-amplifier made a noticeable improvement in sound quality- more than I thought it would. The Lumin volume control was fine, but adding a preamp confirmed my suspicion that I was missing out on something. This made the difference I needed from my system. I’m satisfied with my gear now and will be focusing on room treatment moving forward. I only listened to streaming and my NAS. I haven’t rewired the turntable for XLR yet, but will in the next couple days. I can imagine that results for a preamp will depend on the preamplifier being used. This might be where the "your results may vary" and "system dependent" comments come from. There’s no going back for me. If I had to describe the difference between running direct from the Lumin S1 compared to running through the preamp: with the preamp- more depth, better separation of instruments, more full sound, and better focused center image. The only downside I’ve noticed is it does make a little hiss with volume all the way down from the speakers, but it’s minor. I’m thinking this is normal since it’s a tube preamp. It’s still less noise than my old tube amp made though. I hope you find this information helpful.