Most mic preamps that are bundled in with external interfaces arn't great, obviously some are better than others but its not really worth changing the interface you already have just because of the preamps.
For this reason i would have to agree with the previous posters that you are better off looking for a decent mic preamp rather than another audio interface. As for what preamp to choose, that is another topic and would depend on your budget and the sound you want to achieve.
