I don't know about the sound of the Omni - but I have two of the Aardvark 24/96 units -- and love them. Fantastic sound.
Offhand, the specs on the Omni look good, and its probably fine. It looks like the Omni only has 2 microphone inputs, while the Aardvark has 4. The Aardvark has basic EQ, compression, and reverb available in the interface -- VERY helpful for letting the musician monitor the signal while recording. These effects are built into the interface, and do not require any of your host computer resources. They also don't have any perceptible delay on them, which really helps in monitoring.
Again, the sound on the Aardvark units is incredible. I bought one, then bought the other once I had really tried it out. It is a very clean, clear and accurate sound. If you want a sound with a particular character, you can always plug a different preamp into it.
One issue I ran into was with two interfaces, you need something external to combine the signal for monitoring, or you end up giving up some input channels on the 2nd unit. I use a Samson c-control unit and it works great for that.
-lee-