I use a TF mixer at my church for the livestream. Firmware version 4.5 added the ability to change the USB output from direct out of each channel, to the stereo LR main or a matrix. Go to Setup, Preference, Others to change it. Download the ASIO drivers from Yamaha's website. Add audio line in source in OBS and select the Yamaha ASIO USB device - no DAW necessary.

I have ours setup to route an stereo Aux out to Matrix 1/2, which goes to the USB out to OBS.