I have had a Pioneer AVIC-D2 for a while now, and I love it. It is a great unit. There are newer versions out there, but they all use the same map discs for the most part. And you can get it for much cheaper than the new ones. It is not a flip out, though. It is a full touch screen that folds down and behind the screen is a slot for the navigation DVD as well as a slot for CD/MP3/WMA, etc. You can get the XM or Siruis tuner if you want, but with XM you can get XM NavTraffic, which is pretty cool. You can hook an iPod to it, Bluetooth, rear camera, etc. It is worth checking out in my opinion. Also, in my old Lexus, I had Eclipse speakers all around and they sounded beautiful. Hope this helps.
Do you happen to know what sizes those speakers were? Impedance, size, everything? and do you know if the first gen GS and second gen GS have the same size speakers?
Thanks,
~rob