If you are using the card mainly for playback, the USB 2 bandwidth is not an issue at all. You are talking about two channels (surround would be 5) of output, which is not going to show any difference between PCI and USB2. USB units are capable of recording dozens of inputs successfully. Audio is pretty sparse data by computer standards. And a USB interface will be just as fast on your next computer and can be attached to a new or borrowed computer in a flash.
Assuming your Audiophile 2496 has drivers for your operating system and you have a PCI slot in your motherboard, that will be more than enough for your needs. There may be a problem with a bridged PCI slot in newer computers with that card, but you can try it for nothing to see if it works.