I'm not sure OBS will see the "main output" of PlayIt Live.
As it is often used for application audio & video capture it might but you will have to experiment.
Otherwise, assuming OBS can take a sound card input (I'm fairly sure it can) then you could send the PlayIt Live audio to (say) a USB sound card or mixer then use the USB sound card or mixer as a source to OBS.
The mixer (or sound card) would have to "loop" the incoming audio to the outgoing audio but with that limitation it sounds like it would be practical.
Craig Gaudaur