Hey Guys, I am looking for a new setup for my car but I don't know which power amp to choose.
My (new) setup:
Radio Unit:
Pioneer FH-X840DAB
Speaker (x4):
Ground Zero GZIF 52X
2x 60 W | 4 Ohm
Subwoofer:
Ground Zero GZIB 200XBR
20 cm | 150 Watt RMS | 4 Ohm
I don't want to provide links because I don't want to advertise products, but if you need more specs, leave a message and I will provide.
I'm not going to attempt a specific recommendation, but is it just for the subwoofer? Generally, the woofer/subwoofer needs more power than the midrange & tweeters.
The only "spec" I'd be concerned with is power, but you can't always trust the manufacturer. (If you buy from "cheap" unknown manufacturer they are probably "fudging" the specs.) "RMS power" is almost always more honest than "peak power", but if the amplifier can actually put-out a little extra on occasional peaks, that's not a bad thing.
If you get a stereo amp for a single subwoofer, look for one that's "bridgeable". You're using both channels in a bridged configuration so that's at least twice the power of a single channel, and sometimes up to 4 times the power.
If you trust the specs of the speaker and amplifier, it's supposed to be OK to use an amplifier rated for 150W with a 150W speaker as long as you're only hitting 150W (or less) on the program peaks and not driving the amplifier into distortion. (If you drive the amplifier into distortion you increase the average power.) In other words, you can burn-out an honestly-rated 150W speaker with continuous 150W test tones, and a 150W tweeter is only rated for the higher frequency (lower power) part from a 150W amp.
Beyond that, you can consider the manufacturer's reputation and reliability (to the extent you can find that information.)
Noise, distortion, and frequency response are normally better than human hearing so I wouldn't worry about those specs at all.. But, of course you can get noise from the car's electrical system into the audio system and that's pretty-much unpredictable. And the more gain you have the more noticeable the noise.
It looks like your head unit has a crossover built-in so you don't need a crossover (or high-pass/low-pass filters) built into your amplifier.
Is it even needed though? From googling the sub comes with its own amp already, so I'm guessing the OP wants an amp for the 4x speakers.