Hey Tim:
I removed (and stored) my 91 Multivans original Heidelberg stereo and
installed the following:

Description   Actl Cost

Upgrade
Replacement Stereo - Alpine 9803 - 45w X 4 RMS  $120.00
JL Audio e4300, 45W(RMS) x 4, 4ch amp  $125.00
Alpine KCA-121B MP3 Cable Adapter  $14.99
MP3 Streamer - Rockford OmniFi  $130.00
Replacement Rear Speakers (use front Kenwoods 5.25"
Replacement Front Component Speakers (MB Quart 6")  $115.00
Subwoofer - Infinity Basslink II - 200 Watt  $228.00

This is hands down the most fun stereo I've ever had.  The MP3 Streamer
gives me the ability to synchronize any music on my home pc's harddrive to
the 20 gig harddrive I have in my Vanagon automatically.  No changing out
cd disks.   Also, I have the ability to do a random shuffle of all content
which is nice.
The Infinity Sub is really nice, not boomy.  This system does not have to
be loud at all to sound good.  And, since I got through applying
soundproofing material throughout the van, I can actually leave the stereo
very low and still get very good sound.

Good luck,
Brent
www.weidefamily.net/vanagon/
I highly recommend the setup to anyone interested.