T+A 200 though I have never heard it gets high, high marks from anyone that has any experience listening to one, great suggestion for the OP based on his criteria. Any experience with the Preamp section in the 200, wondering if it’s on par with the DAC.
OP, I’ve tried a decent amount of DAC’s in my system, another poster mentioned this already, noise and power can have a big impact on your DAC’s performance. Part of why the 390 is performing or sounding better in your set up could be it’s reducing the introduction of noise. What you are hearing with your stand alone DAC lines up with what you often hear when you have some noise, jitter finding its way into the chain, and or noise from your power source. If you want made in the USA, in your price range the new PS Audio MKii checks off the boxes for the sonic characteristics. It’s detailed, non fatiguing, smooth but not overly warm like you find with some Tube stage DAC’s or R2R DAC’s. Benchmark makes their gear in the US, they are definitely not known for being overly warm. If you thought you where open to R2R and or Tube DAC’c, LTA just came out with their first in house DAC, they are made in the US and I’ve only heard really high praise for all their gear. Bricasti gets high marks for their DAC’s and streamers, made in US, Chord another US option.
If you can venture outside US, European made, Lumin, Aurilac, Aurender are all companies solely focusing on streaming and DAC’s. Whether it’s a streamer, DAC or all in one box, really hard to beat but believe all 3 brands are made in Asia.
Good Luck,