My UPR cat'ed X-pipe sounds pretty nice, albeit a tad too quiet for my tastes with the Dynomax cat-back I've got behind it. Not raspy at all. I'm about to find out in a few days (when I get the time to crawl under there) what it'll sound like with a pair of Pypes Violator muffs in place behind it.
Of course, a catless X is something of a totally different ballgame, but nevertheless, LT's tend to quiet things down enough that an X, in and of itself, shouldn't cause things to sound tinny or ricey in any way. I'd have to agree with the others above that it's likely those Flows you've got behind it. Chambered muffs without sound packing of any sort have a really hollow sound to 'em, and a catless X is just going to crank the volume up on that sort of sound all the more - some folks dig that sound, others hate it. Maybe it just wasn't as noticeable before with your prior setup...?
Maybe consider some Hooker AeroChambers, if you prefer chambered muffs, or go for any straight-through design muff - Dynomax Ultra-Flo, Hooker Max Flow, Edelbrock RPM, Pypes Violator or Race Pro, Magnaflow, etc. - for something that'll burble at idle and sound sedate at cruise but roars at WOT.