I was just reading about using multi-turn linear pots as volume controls. Reportedly pretty transparent. Don't know where to get a stereo one, though.
https://www.diyaudio.com/community/threads/volume-control-options-for-tube-preamp.384482/page-5
https://www.diyaudio.com/community/threads/volume-control-options-for-tube-preamp.384482/page-5