What kind of interface are you using?
yes, you can...putting a mixer in between will be fine. Personally, I wouldn't do it to change the sound (as far as any effects or processors, I do that in the computer) but I do use one to add more analog inputs to whats going in my computer. Actually, depending on what you're trying to do, you can get a USB Mixer with a built in interface.
check this out... http://www.sweetwater.com/store/detail/M6mixer/
this is the one I use... http://www.sweetwater.com/store/detail/C3USB/
The interface should have phantom power, you shouldnt need a mixer between an MPC and interface though. Just record into the comp and mix there. Way more flexible