Hey,
Turner makes "shorty" headers for the e36, but they cost almost as much as the SS headers. I know that SS also makes a resonator to replace the cat, but I believe it's machined to fit w/ SS's header and extaust system. Personally I wouldn't do any more exhaust work. Its not going to do you that much more good than your cat back unless you have more air flowing in.
Hope this helps.
-Matt