Upgrading Stereo System
 

OK.. So I've got the HU 613 in my '04 XC70 and having been spoiled by a fabulous system in my Murano, (now returned to sender), I'd like to figure out whats the best route to upgrading the thing.

Lots of questions spring to mind:
1. If I buy a new deck (non Volvo), are there any that will retain the steering wheel button functionality?
2. Dosome Volvo decks have an internal multi-CD changer? The way I read the manual, there's a space for a changer somewhere n back. I hate those things as you have to buy proprietary CD cartridges and then there's the hassle of having to go uncover the damn changer toswitch cartridges.
3. Is it smarter to just change out the speakers for the Volvo upgrades; do the doors, etc., need modification for more speakers; should I just go for new speakers in the existing holes & add a sub-woofer & amp?

So many questions, so little money.

Information regarding any questions or conditionsI haven't asked about, but should have, gratefullyappreciated.