Yup, that's about it for 2 ohms. The big (suitcase sized and expensive) amps do invert, so they can pump out the mega watts. The smaller systems (dash stereo etc.) don't have the room for inverters, (besides, they're built too cheap) so all they can do is down-convert from the incoming 12 volts to get usable audio.

My favorite ratings are for an amp the size of two cigarette packs that are "200 watts" riiiight. (Walmart etc.) Maybe feeding a test tone into a direct short, but USABLE wattage to drive speakers without mass distortion? About 5 to 8 max.

As for caps, the typical output cap is 470 uf, and those can be pretty small at the voltages involved. (Probably 15V caps)

Sounds like the OP has it sacked, and the relay's are a good idea. Just don't forget to lower the iPod's volume before plugging it in.