The MobilePre actually has line-level unbalanced outputs (according to their website here).
Many people shy away from unbalanced connections, as if they are some sort of terrible mistake that should be avoided at all costs. In fact, they have their place, just as balanced cables do too. In fact, in this case, over short cable runs at least, they could even be considered desirable!
As you may know, the process of "balancing" involves duplicating and inverting a signal, in order to filter out noise at the receiving end. This process in itself and actually induce some level of noise, which can be undesirable. Bob Katz, in his book on audio mastering, mentions that many mastering engineers will actually modify their equipment to remove unnecessary amplification and balancing sections, all in the name of reducing noise.
This is precisely why audio interface designers tend to provide unbalanced line level outputs. Higher end interfaces will provide digital outputs, which don't suffer from noise in the same way as their analogue counterparts.
Unless you run your speaker output cables in parallel with a mains cable (this actually induce noise even in a balanced cable), you will most likely not get any problems at all.
Introducing a DI box into the equation will increase clutter, increase noise, increase complication, and worst of all, probably not make any difference whatsoever.
Most mixers have dedicated line level inputs for stereo sound sources, just like your M-Audio MobilePre, so I suggest you use these.
The issues of "static" or "hum" in hardware connected to computers is more likely to be caused by poor earthing. One way to fix this is to not rely on the USB connection to provide power - plugging your MobilePre into it's own dedicated power supply can reduce this.
I just noticed that the MobilePre doesn't have connections for an external power supply, which is a shame! For other interfaces that do have an external connection, this can be useful.
Another thing to consider is that your mixing console might actually be unnecessary here - without knowing your setup, it's hard to say, but have you considered simply connecting the outputs of your MobilePre directly to your monitors? This has obvious benefits in terms of simplicity, but removing extraneous equipment from your signal chain can also reduce noise.