Ya, I've actually given them a try with the crossover boxes. Not bad... They could go back in, but I'm mounting them better than with hot glue if I do.
This car came standard with two 10cm door speakers and two 5.25"s behind the seats in speaker boxes. Weaksauce... My AE86 had the same setup. Apparently 5.25s up front and 6x9s in the rear is doable without too much modification. Could I do a decent setup in those sizes, plus maybe some fresh new tweeters and a smallish sub+amp (if I can find a spot for it!), for under, say, a few hundred Eurobucks? I really don't know anything about car audio design, so some hints as to the kind of stuff I should be looking at/for would be pretty useful. My new head unit was cheap and will probably be the limiting factor in sound quality.
I'd love to have the quality of the factory System 10 in my old Celica, but that's probably not going to happen on my money budget OR my weight budget...