Im in a big pickle here

always wanted a car pc and just about to buy one but one thing im very iffy on is the quality
i have found a second hand car pc that im pretty keen on
the mb is a jetway J7F4K1G5D-LF
it comes with all the normal gear as well as some gps gear etc
Im mainly going to be using it for MP3's (winamp) and movies ( VLC or WMP )
Im worried about the quailty and channels
The mb has a 6ch on board sound
My system consists of
pair of splits in the front
6" in the back
2 x subs boot
ALL the gear is being run off amps
How would this setup compare to a $500 deck in the sound quality wise
Thanks
(sorry if this has been brought up before done a search and found nothing)