Questions about EV radio option

1) Who makes this headunit?

2) Does it use a factory amp?
2a) If yes, does it use RCA's from the HU or speaker level inputs?
2b) If it uses speaker level input, what wattage does the HU output?
2c) Would using an aftermarket HU really make a significent difference if speaker level outputs go to the amp?

3) Is the subwoofer (Hal) self-powered?
3a) If the subwoofer is removed will the system still function?

I was considering replacing the door speakers only but after reading through the threads, most say it won't improve sound quality and may even make it worse. Replacing the HU with a rear USB would be ideal, as I use an Ipod.

I'd like to use whatever parts that are worthwhile reusing, for economic reasons. I'm not a fan of speaker level inputs on amps (as I suspect this is).

Thank you in advance for your answers, opinions and advice on this subject.

Jim