When I bought my '98 Taxi, I thought I'd do to it what I did to my 900/6, drill out the baffles in the muffler to increase sound slightly and maybe enhance performance.
After I got the bike home I stuck a piece of 1/2" dowel rod down the opening at the rear of the muffler and it almost swallowed up the 3' piece of dowel. Peering down the center of the muffler with a flashlight, I saw there was no baffle to drill through. That means our OEM muffler is straight through, or at least the one installed on my '98 model.
The cat has some sound deadening qualities but it's straight through too. Looks to me if you want to increase sound, you've got to go aftermarket.
I went with Remus on my '98. It's not too loud, compared to Two Brothers or ZTechnic and it's comparable to a couple of Staintune pipes I've heard.