I have a harmonizer. The TC helicon voicelive
It works fine with my present setup sending data out via midi 5, setting the device to midi 5 and using midi to the Ketron.

I was interested in another post saying Band in a Box cannot do multiple midi devices.

I have no problem clicking use Dxi (Coyote Forte) as the main midi device chosen in the window. I also have a Uno usb to midi device and I select that on both accounts. Running the midi from the midi cable to the voicebox on midi 5 I am able to control the box with commands from the solo track, by pressing F5 and putting in the patch to select the harmony type.

My computer played the Dxi synth and sent midi ch 5 triads and chords to the voicebox, along with commands to change it's operation.

I suspect that if you set other tracks such as the Melody track to use midi 12 going to a lighting console and changing the scene. All that that should be possible, you just need to chain the devices and have them respond on their own channel.

If you have any questions there are others here who have used this type of device.