I think you should be ok. bit depth is basically associated with dynamic range. 24 bits allow you to have a dynamic range greater than 100dB while the best you can with 16 bits is around 96dB. What does this mean? It gives you a more accurate sound, more detail, less artificial. Here is a good explanation.
http://www.pcrecording.com/dither.htm
I used a PCI soundcard folded over the top of my M10K using a PCI rsier card and as long as I didn't run any IDE cable too close to the soundcard I didn't have any noise issues on my analog outputs.