The thing with Bose is that it seems to get better every year. And they probably deteriorate like any other system after 15 years... My 99 Infiniti with Bose was just an alright stock system. (this is comparing to non-Bose factory systems). A 2007 Chevy truck with Bose sounds REALLY good, I thought it had a complete entry level system installed, when in fact it was just Bose. So I can only imagine 1994 Bose sounding like crap.
And dont try to "mix and match" aftermarket parts with Bose parts. It will get even worse. In my 99, Bose HU sends a millivoltage through the wiring which goes to a Bose amp and then amplified to the Bose speakers. They are all designed to work with eachother and shit will get funky quick if you start installing only a few aftermarket parts, like just replacing the deck.
My suggestion: Either remove EVERYTHING Bose and do the whole system at once, or don't do it at all. This is life with Bose.