Solo streamer

RV, FWIW, but as I recall, you have a Schiit Loki. A lot of 'brightness' folks seem to complain originates in the upper-mid frequencies, i.e. 1500 to 3000 hz. Mostly on sources. Your complaint seems to be (logically anyway) coming from your sources and/or the recordings).  I think your CJ may have a tape loop. If so I'd suggest that you put the Loki in the loop and when you encounter that brightness flip on the loop switch and fiddle with the 2K knob some and see if the brightness goes away. You could put the Loki between your source and preamp but that is something I'd not  do if I really loved your source. Maybe a better solution, and a lot cheaper anyway, than by shopping other sources or wires which might just bring you different problems. Good luck.

RV, to help you get away from the electronics aspect of your music, try something I assume you might enjoy, and be a bit new for you. FWIW I've several  transcriptions for piano of Beethoven's Symphonies. Don't know why I have several because, frankly I really didn't connect. I almost missed these Symphonies which are performed by a trio. There are three recordings of them, my first was Sym #4 and the Archduke, The second was Sym #2 and #5, the last was Sym #6. Performed by Emanuel Ax, Leonidas Kavakos, and YoYo Ma on Sony. Music and sound you can just wallow in I think. You rarely hear this kind of chamber music! Try the #4 with the Archduke first if you are at all inclined.