As far as i can make out with pretty much any speakers you can wire them up to an amp. The only thing an amp relies upon though is the signal from you head unit (and obviously power from battery). This usually comes from some phono leads. You dont have to wire up speakers to an amp you can wire them into your headunit. At the end of the day if you have a sh?@ headunit and quality speakers you wont get very good sound but if you have a good head unit and average apeakers you will get a better sound. (hope you can understand what i am writing, it makes sence in my head :scratch: ).
If you have an average head unit, an amp and speakers the sound will be alright.
In my car ive got a Kenwood 7024, and i think its the dog's dangly bits, coupled with a pair of infinity 6x9's, a kenwood component kit, a 10" splx sub and two amps. It runs quite nicely but the front components need to be better.
All an amp does is, very basically, boost the sound and to an extent the sound quality. (It only boosts the quality because if the sound level was coming through the head unit alone, at high volume, it would'nt always be very clear).
Again sorry for affling :lol:
If you want the best though Rockford Fosgate is the light at the end of the tunnel (but expensive.. :| )