The formula of trouble-shooting your system/room, is to change one variable at a time. By process of elimination, can figure out what is doing what - and that included acoustical treatments.
I would suggest working with what you have, and making sure tha the acoustics are right, first. Larger spaces may be easier to get sounding good, long wall setup's, etc, rather than smaller spaces. If so, you might need some acoustic treatments to come into play. Then, once you know your acoustics and setup are secure and balanced properly, you can start swapping out gear.
On that note, I would start with cheap fixes like cabling. Then I'd adress preamp and amp combo's. The speakers are a large change, and will likely have the most dramatic impact on sound. But then, you do already have those, and need to set the room up around them first. So, I'd likely change those last, if I couldn't get the sound I wanted after doing the following, first:
Acoustics check, setup check, speaker wires and cables check, tweaks check, preamp check, amp check, then speakers as a last ditch.
Of course, you could just start with another pair of speakers, but sounds like that might not be your biggest issue. Probably acoustics, setup and system matching.
good luck