Just reiterating what others have said
- Make sure to add delay to the SBD feed, I always do an estimate of how far my mics are from the stage whenever I get a SBD feed and I almost always add some delay to make sure they are in sync, even it was less than the 30ft recommendation that was previously given
- Add reverb to the soundboard file to your taste, it can make a big difference in how the mix sounds with the Aud source
- Depending on how the vocals or other instruments are in the SBD mix, some can be overpowering, use some compression on the SBD file, start off with less and increase and see how it sounds, this can also make a big difference if vocals/instruments are more pronounced in the mix and need to be brought down
- Add some EQ ( i typically use a 30 band) to your taste as your mixing to either track, or with the final mix, whatever your preference is there