Yeah if they're decent hi powered 6x9's an amp i reccommended but not 100% necessary If you havent got use of a parcel shelf you can get 6x9 boxes which might be more practical?
Easiest n/a swap to do would be 5efhe. If you can find one. Then bolt ons flywheel head work n ecu, then strip the hell out of you car With out going custom engine conversion 150 160ish bhp is about your limit imo
Boxing them in would help but the main issue is they face the floor which sucks! Ideally you would want some 16cm ones in the doors but that means pods and wiring to be sorted. Easiest way to get better sound chuck some 6x9's on the parcel shelf or if you dont have one in a box behind the seats with a small amp to power them.