I bought a B&B for mine, but I don't know if I'd spend the money again. If I did, I'd probably spend a little more and get an Eisenmann, lol(best sound IMO). There aren't many options so you're probably just better off picking a universal muffler and having a shop make something for you.
I've got the exhaust, MarkD chip, JB racing flywheel and a 3.15LSD and to be honest even with all that stuff it's not much different than stock to me. Mind you, those mods came gradually and the car was out of commish for a while, so maybe it'd be more noticeable driven back to back with a stocker.
You say it's running fairly well, but I'd spend my first several hundred bucks on getting it running tip-top: Intake manifold gaskets, PCV plate/OSV, valley pan gasket, valve cover gaskets, vacuum lines, any finicky sensors, etc. If these things haven't been done you should notice a huge improvement right off the bat. Chances are, unless you bought the car off a total fanatic, it needs at least a few of these things.
Also, drop your lower oil pan and check it for oil pump bolts/nuts, unless you know for sure that the PO already addressed this issue. It's pretty common from what I can tell.
Finally, if you haven't already, head back on over to BFC and search around the E34 section. Pretty much any question you can think of relating to your new ride has probably already been answered there. It's a great resource.