input levels and mic gain

[Rotti]

I'm having a problem wth my recording setup. I have five drum mics on an acoustic kit. One snare, one tom, one floor tom, and one bass drum(all with a couple of inches of the skin). Plus one overhead condensor. The overhead is fine but I'm having a problem getting a low enough input level from the drum mics to my software.
I run the four mics into a Behringer micro mixer then into an M-audio DMP3 preamp, then into an M-audio 24/96 sound card. I am using Sony's Vegas for recording.
The micro mixer levels are about half, the dmp3 level is all the way down and I'm still clipping or very close to it. Is there a way to lower the input level in software? I can choose "mixer" as my input in Vegas preferences instead of inputs 1&2 . This lets me control the input level with the m-auido mixer software but then any other tracks that are beig played back while recording, like guitar or bass get blended into the drum tracks.
If I turn the levels of the micro mixer all the way down it seems the sound quality really suffers. I'm not sure but I think it sounds best when there is a fair amount of gain or sensativity on the mics. But then I clip and get distortion.
I should add that the reason I am using the micro mixer is so that I can mic the entire kit at once and record with only two channels. One channel for the overhead and one for the four drum mics. The micro mixer allows me to balance the level of the four drum mics and put it into one channel. Not perfect but I'm trying to make do with what I have.