[lancemcv]

I would look at the Mbox pros system pref which has its own mixer and it's running in the background whenever you use the mboxpro. There are things like a stereo enhancer and it adds noise, it should be preset to off position.
As far as I can tell it is only a monitoring thing and does not effect what is going to disk but may add noise to the stereo buss.
But you are most likely just getting hiss from the plugins your using, you can hold down the option and command keys and click on a pluggin and all the plugins inserted in the same insert should all be deactivated and you should hear a drop in the hiss, if you do then you know it is the plugins that is causing the hiss. Using noise reduction on your mix is not the right way to fix the problem. Maximizing the mix will bring the plugin hiss out even more as it limits the peaks and brings up the lower levels and floor noise.

in response to '"why 88.2 24bit"
As apposed to 44.1 or 48??

88.2 is twice the sample rate of 44.1 so you are capturing twice as much samples per second. Then when you make a 44.1 16 bit master you add dither to remove the hiss caused by truncating the samples. In the end it makes for a better sounding recording. Tracks some drums at 44.1 16 bit then do the same with a new session at 88.2 24bit. You should be able to hear the difference. Live drums tend to sound more life like and less like samples. Theory has it that 88.2 is better than 96k if you are making a final 44.1 master because it is even math to just cut the sample rate exactly in half.