2005 roadster limited with infinity factory head unit. My head unit acts up in hot weather when playing CD's. after playing for awhile, 1st sound quality gets poor and then the unit will shut off. If I take out the CD it is actually hot. I am ready to change out/upgrade the head unit anyway. Can anyone verify from description it is head unit and NOT Amp? This did not start happening though until I changed out the component door/dash speakers with 4 ohm speakers. It wasn't an immediate thing though so could be coiincidence. Or this could be causing my amp to overheat?

Another thing I'm confused about - 2 ohm vs 4 ohm speaker AND the effect on the factory amp. The factory speakers are 2 ohm. Virtually all aftermarket speakers are 4 ohm. Right now I have 2 ohm rears and 4 ohm tweeter/doors. (I changed them out when 1 door speaker blew) Now I have a blown rear woofer. Questions:
1. could this damage the amp and/or head unit?
2. Do any changes need to be made to the factory amp to work with 4 ohm speakers?
3. I still have all original speakers. Am I better off replacing blown door speaker and rear speaker with stock and replacing head unit? I'm guessing head unit don't care bout speaker ohms because I am pre-amping out to factory amp.
4. Or. Is the 2 ohm 4 ohm thing not matter as long as they are all the same? (I know 2 ohm speakers are much more efficient) Is amp still adequate?

I want to continue to use the factory amp(because in this forum I found it is used for things other than the radio?)