Sorry can't comment on in-cabinet designs - I have in/on wall design. However just a suggestion to consider going with a vertical center channel speaker if you can accomodate it instead of the horizontal. Suggest M80, M22 or M2 (in that order) to match L&R M80's.
Or if you want/need to go horizontal center consider the VP-180 to match the M80's.

Last edited by cb919; 04/07/11 06:08 PM. Reason: forgot the big 180
Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1