Power is the most important thing in a carputer, and for all the things you have mentioned you want it to do, the Opus will do it.
You've got two choices:
1. Spend $200 on an Opus
2. Spend $40 on an ITPS, find it doesn't work like you want it to, spend $50 on other stuff you've seen elsewhere, then spend $200 on an Opus
With regards to the DVD, you could possibly run an IDE cable back to the computer (a couple of people here have been using a 15ft cable OK) or you could get a FireWire or USB2 IDE adapter and run a FW/USB cable to the back