Andy, I have a Best Mufflers dump pipe with std system from there back. I personally wouldnt think of replacing my mufflers; I'm sure I read on here somewhere that the MPS6 mufflers are "a marvel of engineering excellence" (or words to that effect) being very efficient and causing minimal power loss while avoiding the dreaded drone.
Not exactly sure if you are looking to go back to standard MPS6 mufflers of if you are looking to replace the standard ones. If you are looking to have your car produce a "bit" of a note but not make excessive noise then I can highly recommend the dump pipe. (The performance gain is not to be sneezed at either.)
I live in Newcastle. PM me and we can arrange for you to listen to how your 6 would sound with a dump pipe before you go to the expense of exchanging your mufflers.
Leon
Started out with nothing Still got most of it left