Will Aftermarket Head Unit (Stereo Deck) Work With Stock/Factory Parts (Amp, Sub, Speaker)?

I'm thinking about replacing the infinity factory stereo system in my car, mainly trying to replace the head unit first. What equipment would I need to replace the head unit? Dash Kit, Wiring Harness and anything else? I read somewhere that an aftermarket head unit may not work with stock speakers, amp etc. I have an 06 lancer ralliart if that helps and an infinity stock amp under the driver's seat. Any tips and opinions about the whole entire stereo system (amp,head unit, speakers, subs) would help a lot! Thanks!