You can put a double-DIN head unit in a NG900, but since you don't have quite as much height as you do in a 9-3 with the cup holder removed, you can't use a standard double-DIN trim ring. You basically have to cut off the top and make it u-shaped. Depth is also a little bit of an issue. I used to have a Pioneer AVIC F700 in my '97 900, and the wiring was very tight. I had to pull out the ACC panel, pull the wiring down below the radio, slide it in, and then make sure the wiring didn't interfere with the ACC panel. Now I have a cheap Pioneer double-DIN media receiver, which is very shallow, about half the depth of a standard double-DIN head unit. There are no issues with wiring with that one, and I was able to use a pre-made Pioneer to ISO adapter from Amazon to wire it up. You can also keep the factory amp, but you have to be handy with a soldering iron and make up an adapter cable that converts the factory DIN plug to a pair of RCA jacks and a turn-on lead, which connects to the amp or antenna trigger on the head unit. I have my door speaker amp hooked up the subwoofer output on my head unit, which works great.
This is an old post I made on the subject, but unfortunately the pictures no longer work:
Today I finally finished the installation of a Pioneer AVIC-F700BT double-DIN navigation radio that I started last Saturday. Here's the long story of yet another radio installation in my Saab: Wiring: I bought a cheap VW wiring harness off of eBay to hook it up with. Like a lot of others have...
www.saabcentral.com
Another great source of information on audio upgrades for these cars is Richard Bevan's Saab Audio Guide:
