I haven't taken my LS exhaust apart (I've been hoping, praying and doing everything to keep it together!) but I do think that the LS mufflers use baffles only. Mine has also recently gotten a bit louder I think due to what was formerly a loose rattly baffle finally rusting enough to come apart... It was a bit anemic sounding originally, so I don't mind.
These exhaust systems are very hard to come by, and I do not know if it is possible to get baffles to fit or if one must look for an entire muffler assembly. I also am not sure if the baffle from the stock chrome mufflers will fit the black LS mufflers, though I think that they should ?