cat back or MORE?

[Festively Jolly]

hey list.   after a single year's use of a new OE exhuast, it needs
replacing.  the car is a 1988 Audi 90 FWD.   i want free flow (or do i?)
for a little more power.  should i go cat back or more than that?  i
dont understand how just a cat back can erally improve things.  i would
think a person would have to do it right from the engine.

any good info out there?  brand names or sources?
thanks a ton