I don't really understand what your problem could be. Is your room acoustically treated? The tone controls, if that is what you are referring to, will be applied across all the channels in surround mode. They are only able to make crude adjustments based on your listening environment and the automatic EQ's offered by some recievers would be more effective. Personally I'm not too fussy about sound quality and make do with tone controls. You could try enabling cinema/THX EQ as these are designed to broadly compensate for the fact that you are not listening in a dubbing theatre. I've certainly found cinema EQ effective in removing the excessive brightness of film soundtracks.
In DTS mode, you should get sound quality approaching, if not exceeding, that in a cinema. Unless you have a very large room with acoustical treatment, I can't see that you will get much improvement buying separates.