I recommend m-audio too. A word of warning, many soundcards with a digital output will resample the signal before sending it out. For example the Soundblaster Extigy resamples 44.1kHz signals to 48kHz. This sounds bad. The m-audio cards don't have this problem. Look for "bit-for-bit digital output" or something like it on their website.
On the question of whether to go with a internal or external card. If you are piping the digital signal to an external DAC then use an internal soundcard with an S/PDIF output. USB interfaces take use up processing power and the sound will skip when the computer is being used intesively (oddly enough scrolling a window is a processor intensive operation). But if you are going to use the analog ouputs of a card then definately go with an external soundcard. It will sound much better. The internal soundcard gets interference generated by the computer.
If you go with a digital out, I've had good luck with jitter reduction devices like the Monarchy DIP. Evidently soundcards don't output the cleanest digital signals.
On the question of whether to go with a internal or external card. If you are piping the digital signal to an external DAC then use an internal soundcard with an S/PDIF output. USB interfaces take use up processing power and the sound will skip when the computer is being used intesively (oddly enough scrolling a window is a processor intensive operation). But if you are going to use the analog ouputs of a card then definately go with an external soundcard. It will sound much better. The internal soundcard gets interference generated by the computer.
If you go with a digital out, I've had good luck with jitter reduction devices like the Monarchy DIP. Evidently soundcards don't output the cleanest digital signals.