Actually you do not even need an amp and sub, I run an Alpine HU and 4 Eclipse 6.5" 2way speakers.
The SQ including bass response is very good, to the point that I have been accused of having a hidden amp and sub.
I spent a lot of time and effort on the speaker install, front speakers are mounted to custom MDF speaker housings, replacing the stock plastic ones and the doors are Dynamated, including replacing stock vapour barrier with a single sheet of Dynamat.
The rear speakers are mounted in custom MDF and fiberglass cabinets, replacing the stock speaker mounting plates, some Dynamating was also done in the rear.
All the wiring is stock except for a 12ga power lead for the HUs constant power and about 12" of 16ga speaker wire in the rear cabinets.
Both sets of speakers are behind the stock grills and the tweeters are disabled on the rear set.
This system was designed and installed for two reasons, first, as a demo for what can be done without amps, [off-board] and subs, second, because I autocross with my car and weight was an issue, and I didn’t want to be pulling a sub box and amp every time I race.
What I recommend is something like the above, use Eclipse SP6500… http://www.eclipse-web.com/point/sp6500.html [it is what I will be replacing my 7yr old 2ways with] remove the tweeters in the rears, find a 4x75W RMS amp, wire the rear speakers in series for an 8 ohm load and bridge the rear channels of the amp into mono.
Time and effort will have to be spent installing the speakers to get the best possible sound from them, the stock speaker mounts just don’t do it.
If after the install you still need more bass, [sub bass] then add a sub, and rewire the rear speakers to the HUs rear outputs and use the amps rear channels to drive a sub.:idea:94