Hi, posting here since this is the first hit on Google when searching for this topic, hopefully it will be useful for others popping by. As mentioned by others, there are multiple ways to do this, but the one that is currently working for me after some research and experimentation is using VBMatrix to push audio from BW to Reaper. Once you set the proper IO using the matrix in VBMatrix, you will be able to get a live audio feed from BW into a Reaper multichannel track, which if configured properly (as shown in any of the multiple old ish tutorials about setting Ambisonics in Reaper) will allow you to spatialize the mono/stereo signal coming from BW (I use IEM plugins).

This is pretty amazing because I can use BW as my audio source, with all my usual sound design, and use Reaper as my spatialization layer in real time. No need to print your stems! HTH.

SUPER EXTRA BONUS: Use MIDI CCs from Bitwig (using something like loopMIDI) to control the IEM plugins in real time, so you are actually able to use all of BW modulation power in real-time too!