You may already be aware of this, PS Audio has their own forums. Here's a link to a thread on tubes for the 300s:
https://forum.psaudio.com/t/since-my-first-bhk-300-thread-got-sort-of-hijacked-heres-mine-on-evaluat...
There are probably others.
https://forum.psaudio.com/t/since-my-first-bhk-300-thread-got-sort-of-hijacked-heres-mine-on-evaluat...
There are probably others.