Man, are YOU asking the wrong guy!!! lol.
Seriousley, even though I'm into this whole detailing thing over 3 weeks, I'll give it a trey: I have the standard 5" attachment that the PC comes with....most of the pads (as I understand it) will fit that size nicely, if they're tight/snug on the 6" then they'll overlap even more for extra protection on the 5" (I believe they stretch).
I think I have the hook attachment (it came with the PC) and the SONUS thing comes with the velcro stuff (?).
Again, I just ORDERED mine and haven't used it -- probably this weekend for the 1st time. Check out Dwayne's EDGE pads here and the PC links elsewhere -- if you can't find them, post it here and I'll try to copy them. Look for some of my threads in this area of DC specifically titled "Porter Cable" etc. I asked a bunch of basic questions on this a week or so ago and some of the Vets were kind enough to post plenty of links.