Your Prochamber is going to quiet down any muffler you put on there, and by quieting down I mean deepening the sound. Also the Prostreest are meant to be used with cats to minimize any rasp. So you could try and swap an aftermarket catted X or H (with only two cats) and see how you like it. Of course that would be more expensive than replacing the mufflers alone...you could always look into 1 chamber flows or SLP resonators.
I'll look for this thread with a mean as hell Prostreets setup on an offroad X I heard a few weeks ago. I'll post the link as soon as I find it.