Right now I have the Audax HT kit surrounds in side columns and in custom DIY angled front baffle ceiling speakers for the rears. The lack of exact timbre matching hasn't bothered me yet but I will admit that I have given some thought to doing a tall slim version of the 3PI for the side surrounds, Something that is just deep enough to hold the drivers. Not that I feel I need to right now but just because it is something I could do.
Here is a shot of my DIY rears, I copied the concept from a Triad Speaker. It got covered with fabric.
This was the inspiration for the rears, I also have some acoustical treatment in mine but it is not obvious in the picture.