I currently have the following set up in my FD2...

Standard 6disc HU
Boston splits front and back
2 Sony 12inch subs
4ch x 160wrms each running front and back, mounted on back of rear seat.
3000w fusion D monoblock running the subs (850wrms x1) mounted on boot floor.

To use the standard HU I just added line level converters to make the speaker wires into RCAs.

I find the sound quality quite decent. I have quite a lot of sound deadening in the boot area but I def need more around the parcel shelf. I dont have any in the doors and havent heard rattles.