You've actually got 4 inputs on your audio interface that can be used to record line level signals.  You could do something like record the stereo out of the house board on inputs 1/2 and then put the direct out from the vocal and  bass on inputs 3/4.  (doesn't have to be vocal and bass, just used them as an example)  Then, you'll have a little more control when you mix.

Better yet, borrow or invest in an audio device with 8 analog inputs.  You'll have a ton more flexibility tracking the direct outputs from the board and you'll be able to do a much better mix of the band.

Another idea

If I was close to the stage and away from the house board with your current setup if ya have 4 inputs

mic guitar cabs for yourself 
pull the drums and vocal mix from the house

throw the bass and drums on a stereo track
all guitars on 1 track
vocals on the last track

Itll give ya a little better mix to work with