Well, I know essentially nothing about the Terratec, so I'm not much help there. However, I do own an Audiophile 2496, and I'm currently replacing it with an external converter box. It sounds quite nice, and works quite well with no driver problems or drama (
Cubase VST32/W98SE). But my finding has been that it can't achieve its specified level of audio performance inside my computer: it misses by quite a lot on S/N.
The problem I have with it is that the noise floor is entirely dominated by digital noise bleedthrough, which I find to be extremely irritating, and the noise level is a great deal higher than the specified -104dBFS. I do a lot of work in acoustic music where the reverb tails and whitespace are important, so the presence of pitched digital wheezes and whines down there drives me *nuts*. Other folks might never notice this, so your mileage may vary.
If it weren't for that, I'd keep it going. As it is, I'm really keeping it only for its MIDI interface.
One advantage to the Terratec: switchable -10/+4 analog I/O. The Audiophile is -10 single-ended only, so I ended up buying a bump box so that I could drive my system properly (the rest of which is all +4). One disadvantage- the MIDI interface appears to be an added-cost option.
I've never seen a picture of the Terratec card: does it have a shielding can over the analog electronics, or any effort made to control EMI pickup from inside the computer? The Audiophile has no additional shielding beyond the ground plane in the PC board: it just hangs all that stuff out there naked in the breeze. A PC board design with a decent ground plane, and a conductive shielding can to complete a Faraday cage around the analog stuff, will have a *much* better chance of controlling the EMI crud that will provide the true in-system noise floor. Of course, better yet is to locate the converters in a completely separate breakout box with a completely separate power supply, but that's not what either of these cards do...
IMNSHO, the Audiophile is a prefectly reasonable sound card for gaming or noncritical home theatre work. It just won't work for me in my particular studio application- I'm fairly hard to please. But don't let that discourage you: find a way to give one a listen, and decide if that would impact you with your working style.