Modification to Solo Mach-X?

Hey guys, I have a set of American Racing Longtubes with high-flow cats running into a solo mach-x system on my R/T. I like the sound but wouldn't mind making it a little deeper. Has anyone swapped out just the muffler portion of the Solo set-up to change the sound at all? Or if not, can anyone suggest good mufflers I could swap them out with? I will be keeping the remainder of the catback set-up if I do make a swap, just want to entertain the idea of changing the mufflers.

Thanks!