If you have infinity kappa's white cone 6x9's i think they are 70w rms, if you buy a good 4-channel amp with real rms of 4x70w you are looking at around £70 to £100, don't buy cheap rubbish off e-bay and keep clear of amps claiming silly power like 4x500w etc as a good 4-channel amp will take a fuse of around 30a at least, The cheap ones on e-bay claiming silly power of 4x500w take a 20a fuse? (says it all!!) at the end of it all you get what you pay for and its well worth spending more as it will last along time,