Welcome!
First of all, I would mirror ARCuhTECH's excellent advice.
And I'll only add that, according to:
auna Boomcase X8 Passive Car Subwoofer | auna-multimedia.co.uk
...it seems you'll need 300 watts RMS (not 600).
For that, you can't go wrong with a R500X1D (one channel, rated at 300 watts RMS at 4 ohms / 500 watts RMS at 2 ohms):
https://www.crutchfield.com/p_575R5...wdv=c&awkw=r500x1d&awmt=p&awnw=g&awug=9002960
First of all, I would mirror ARCuhTECH's excellent advice.
And I'll only add that, according to:
auna Boomcase X8 Passive Car Subwoofer | auna-multimedia.co.uk
...it seems you'll need 300 watts RMS (not 600).
For that, you can't go wrong with a R500X1D (one channel, rated at 300 watts RMS at 4 ohms / 500 watts RMS at 2 ohms):
https://www.crutchfield.com/p_575R5...wdv=c&awkw=r500x1d&awmt=p&awnw=g&awug=9002960