aftermarket radio

So I've had enough with the factory radio. Yesterday while I was driving the volume was at "2" and without touching anything it went to full blast all on it's own.
The radio was already replaced once by the dealer for similar issue.

I found an installation kit on EBAY.
http://cgi.ebay.com/RADIO-INSTALL-C...ameZWDVWQQrdZ1QQcmdZViewItem#ebayphotohosting

And I found the radio I want (JVC indash CD/DVD 3 inch screen)
http://www.circuitcity.com/ssm/JVC-...30532/catOid/-13089/rpem/ccd/productDetail.do

I have a question for anyone who has replaced the factory radio. I'm assuming that I'll lose the function of the steering wheel controls for the volume etc.....
Am I correct?

And if anyone has installed a sub woofer where is the best place to run the main power wire through the firewall?

And where is a good spot for the ground wire for the amp? I hooked up the ground wire to the metal cargo tie down bracket on my MKIV GTI , can I do the same on the MKV?[/