Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
Yea you can, just connect the sub out to the amp, and then get an inverter(a good one) to run the car amp. Is it a good idea? It may not sound the best but I did this one time with two Cerwin-Vega 10"s and it was pretty good(though I used a HT receiver to power the speakers).
It would be easier just to sell the equipment and buy a HT sub with the money.