Just looked at Rockville. What a curious little HTIB...Never imagined a sub and receiver in the same chassis!
First of all, I would move that little sub into a corner. 8” is very small, and it would benefit from boundary gain. Moving the center out away from the wall could help if it’s getting too much reinforcement from the wall, and that closet space could definitely be making the sound funky. Not sure about that whole situation. Could be the other speakers/sub are set too loud and drowning the center out. Could be a poor speaker design. Idk... Having the rug should help, but maybe you should even have a thicker one.
For typical speaker set up, the AVR will emit a test tone and you set each speaker/channel to output at the same level. 75 decibles.(db) when measured with an spl meter(or autocal system) Then when listening to movies and music, the playback levels for each speaker are at the volumes they are supposed to be at. Rockville has a setup video listed, but I couldn’t get anywhere with it.
Edit: just looked at the manual. Useless!
Im guessing you don’t want to move the sub/receiver since you have wire races all over. But I would...because...bass!