Interesting. As far as I know, there is no version of the TTS-1 soft synth that works on a Mac. The TTS-1 is offered by Cakewalk by Bandlab which operate only on Windows.
Band-in-a-Box for Windows and Band-in-a-Box for Mac handle audio and MIDI differently.
Band-in-a-Box for Mac audio and MIDI settings can be accessed on the top menu by navigating to Options > CoreMIDI AudioMIDI Setup ... or through the keystrokes Command+M.
The menu item opens the Apple® Audio Devices and MIDI Studio dialogs, which control the system settings for audio and MIDI. There are two separate windows for Audio Devices and MIDI Studio. Each window has its own Apple Help topic, which opens by clicking on the [?] button.
I found this information in Chapter 1 of the 2022 Band-in-a-Box for Mac online manual
+++ HERE ++++++ Chapter 10 +++ describes recording and working with MIDI using BiaB for Mac.