I'm not aware of a third-party manufacturer that makes a center channel bar that incorporates the slim design, however may can be slim and I would recommend looking around to find a product that aesthetically fits for your solution.
Our soundbar would be a fit, however it isn't 7.1. The width would be approximately 2.5 inches deep, so you might want to look for those specifications.
Does that help?
Does anyone make a speaker system as slim as the ultraslim tvs? we have ours mounted in a cabinet that is 2 1/4 inch deep and would like a center channel speaker compatible with a 7.1 system. thanks, gtb