IIRC, when I worked with TTS in a multi-timbral setup, I would go into the midi tracks and set the inputs to NONE when I was finished working on them. That way, they would not "hear" the midi data on the midi bus and could only use the data stream from the track it was supposed to be listening to.
As I needed to work on a specific track I would set the midi input to the channel my keyboard controller was transmitting on so I could hear what I was doing. When I finished, I turned it off by setting the inputs back to NONE
I always used channel 6 as opposed to OMNI. Just a random choice of channel number.