To give an advice, you'll probably get better results by pluging the phono pre-amp output directly to a digital recorder such as Tascam DR models or Olympus LS10.
It allows you to record at high quality rates and, to my sense, be surer to have the most accurate perception of what goes in to a digital conversion. And you can use them as microphone interface or any portable sound usage. Great though that will of course be more expensive than a M-Audio sound card.
Anyway, for hifi stereo recording, I'd rather invest in a dedicated material, than in any presumably high-end or X-fi computer audio-card. The simplest will most of the time be the best.
Be sure to have good cables (short if possible) and the lesser/fewer material between your Phono and the recorder : it's the better way to have good sound, even with 16Bits rate.
A link that reminds clear things about sample and bitrate :http://www.tweakheadz.com/16_vs_24_bit_audio.htm