I hate to tell you that this plugin will not work within Bitwig.
I also purchased this plugin and it has never worked because it's loaded with bugs. Plugin parameters do not link with the bitwig's, for instanse - if you change the cutoff filter in the plugin GUI, it won't register on the cutoff filter on bitwig plugin readout, there's no link. So it's totally usseless - unless they fix this problem.
I've sent SoundTower emails, but they don't care....so good luck with that.
But if you want to try it out for yourself, then try this :
1. Create Instrument track and create "Hardware Instrument" as your instrument
2. In the "Note FX" insert the SoundTower Pro3 plugin
3. Select your Audio IN channel for the Pro3 on the "Hardware Instrument".
You should hear the Pro3 play through the plugin, if not - then you should double check if your parameters are correct in the Pro3 Global settings, make sure that you have them correctly configured to USB or DIN MIDI, depends on how you connect Pro3 to the computer.
P.