As long as it still works it is most likely not damaged, you probably took some time off its lifespan though. Do you have adequate ventilation around the back of it? If not you might want to consider adding a fan to help keep it cool.
US Acoustics makes very good amps for very little, I've never heard a single bad review of one. A 4 channel with 60x4 will run you about 150 and that will be ok for those Infinitys.