You could use a secondary PCI card, but there are some gotcha's with AIW cards. When I've used a secondary card with my AIW's, it disables video-in functions while the secondary card is enabled. Not really a bg deal unless you want to edit video AND capture video at the same time, or if you want to watch TV on your PC while the secondary card is enabled. There are other issues concerning 3D acceleration on your secondary display as well.
nView looks very promising to me, if nVidia can work out the wrinkles with Personal Cinema, you could have true dual head AND great multimedia features, but they have a lot of wrinkles to work out there, I wouldn't hold my breath.
Another option is to simply add a Tv wonder or Hauppage card to a dual head card, but you'll have to give up some major functionality going that route, If you don't need or use the extra features of the Rage Theater Chip, might be the way to go.