Tubes Everywhere!

Great amps. "classic tube sound"

I've heard them with many nice speakers.  Since it's really subjective, I don't think they project a "tube sound" They're a hybrid, so it's only going to approach "that sound"

It just has a pair of 6DJ8's, so I would buy a few popular  models, and tune to your ears.
https://upscaleaudio.com/products/tungsram-pcc88-7dj8
I believe you have to configure jumpers to accommodate the 7DJ8 

Here's a link to the 6dj8 page of Brent Jessee's website; he provides some takes on various 6dj8s including the equivalent tubes e.g 6922 . Might be helpful to you.

http://www.audiotubes.com/6dj8.htm

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.