As far as the speakers go, you could do but the volume will be difficult to balance and I think the RLs will add little to the quality.
Agreed here - the Beolabs don't put any load at all on the Beocenter, so in theory you could add even two pairs of passive speakers (with the same caveats as in my previous post above)... but I can't see what good it would do.
Regarding the noise, check first that the mechanism is free to bounce on its supports. You should be able to press it down slightly at each corner when the lid is open. It's easy to slightly mislocate the springs etc. while reinstalling the mechanism or closing the top cover.
Other than that, I think a likely suspect might the freewheeling part of the clamp, on the arm that swings with the lid movement. Guess you could try a minuscule amount of sewing machine oil there (you don't want it running down and spreading everywhere while the CD spins).