Welcome Steel,
From what I've heard, the inwall/onwall speakers were designed to give you similar performance to their bookshelf/center big brothers. I'm guessing a step up to the m60's or 80's would give you better overall bass. However, the 500 is an incredible sub, so you would most likely be fine.
Maybe some of the others can give you input, on comparing the m22s/w22s and m150/w150 as I have not had that chance yet.
Keep in mind the onwall speakers will require a bit more contstruction and wiring to accomplish, but that should not be a big deal if your in the middle of construction.
What are you driving the system with for a receiver?
