Not happy yet

I have recently discovered "hi-fi" and have been replacing a few parts of my system. But I have not yet got the involving sound I am looking for. My judgement of the sound: the bass is too loud relative to other sounds, and the voices aren't prominent and involving enough. The loss of tone controls in my new higher-end pre-amp and amp (replaced older receiver) means I can't throttle the bass back as I used to do.

Any advice on where to go next? Here is the equipment:

Yamaha CDX-410u CD player (older single-play player)
Classe CP-35 pre-amp
Rotel RB-981 Power amp
Celestion S300 speakers
Cabling is generic

Room is about 12' x 25', with 8' ceiling. The speakers are at one of the room, several feet from back and side walls. Bare hardwood floor, bare ceiling, fairly sparse wall decoration.

Music is mainly Jazz, older rock, folk. I notice the well-recorded jazz sounds pretty darn good, very good highs, decent voices on the best recordings. Jazz tends not to be bass-heavy to start with.

Any ideas on what the next upgrade or change (room treatment?) should be? I have to go one thing at a time, but I expect to replace almost everything (except possibly the pre-amp and speakers) along the way.

Thanks for any advice...