What is this setting? Default is low I have set to high. I have major output quality?

If your machine doesn't have any problems playing the song, you can leave that on high. I have BIAB on a backup machine that is slower, and I find that it works smoother to set it to Medium on that machine.

Notice where this is, in the Preferences, RealTracks. The options right above and below are also for adjustments to make BIAB run on slower machines.