Carl, there are a couple of things to keep in mind with the Korg M1 Legacy. One is that the latest version is 64 bit so you may need a wrapper to use it.

Another is that you have to set the MIDI in channels in the M1 to match BiaB's MIDI out channels. Also you may have to send a MIDI volume message at the start of the track, that is a CC7 message.

Lastly the M1 only has 8 MIDI tracks in its combo mode so you can only get 8 different sounds going at the same time. Thus you are not going to get all of the GM sounds in one M1.

When I use the M1 Legacy like you want to in Sonar however I have to manually set it up for each song. In fact other than Sonar's TTS-1, which is a GM synth, I have to set up all of my VSTis for each song.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware