You can mute any channel, including all of the MIDI generated channels, leaving just the one audio channel. Right-click on the radio button for each instrument and you will see the option to mute. I could be more specific if you told us what version of BIAB you have, and for what platform - PC or Mac. It might also be solved by using the mixer for your soundcard, depending on what soundcard that is.

For more than one audio track to record yourself, Real Band would work well.

And - Welcome to the forum. In the future, it would probably be better to start a new thread with a new question such as this. Good luck!

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.