I'd try some tube rolling first. That can change the sound of a tube amp enough to make you happy. I have a similar power-level tube amp for my home office and with my 90dB speakers, it sounds great and I have enough power for the room, IMO.
The speakers might be rolled-off in the upper registers due to no tweeter. I'd look at just trying different speakers to see if that reveals anything that you might be missing. The rest of the gear might be fine.
I'd try a few different used bookshelf speakers and see what you discover.