I've botched a number of recordings in small chatty bars with onstage mics doing an "on the fly" matrix where the sbd feed was all vocals and drums and way overpowering, sometimes even brickwalling the vocal preamps on the sbd. And then again, I've made some of my best recordings using the same setup when the sbd mix was better, it's a crap shoot really. I think mixing the onstage mics and sbd post-recording would be best but that's not how I roll; it's all or nothing for me.