Man, Volvo's like this BEG to have their radios replaced with an empeg and an aftermarket AM/FM/CD. I'm surprised that an '03 Volvo still has the double-DIN like the <2000 models. But if it's anything like my 2000 Volvo V70 install
then it will be the easiest thing your car audio installer has ever done.
empeg + AM/FM/CD headunit + PIE MPSS4 source switching relay + amp + factory speakers = simple and very flexible setup. The relay is a box which sends the audio to the amp from the headunit that's currently powered on. On the PIE MPSS4, if you have empeg as primary and radio as secondary, it will work great.
Oh, and the photos in the link above are from the crappy version of my install. The empeg looks almost factory stock with the dashboard plastic, but make sure the installer recesses the second head unit into the dash a little. That way, it won't stick out and look ugly, and you can make a fake stock radio faceplate
to cover the hole in the dashboard when your empeg and headunit faceplate are out.
Rock on with your empeg installed Volvo!
110gig MKIIa (30+80), Eutronix lights, 32 meg stacked RAM, Filener orange gel lens, Greenlights Lit Buttons