Output confusion

I have my main output in the DSPMixFX set to Mix4L/R. I use Reaper and I still have to choose Mix1 when playing a file. If I choose Mix4L/R in Reaper, I get nothing.

It seems like the Streaming button in DSPMixFX forces the output to Mix1 ?

Reaper is using the ASIO Yamaha driver. I have DSPMixFX main output to Mix4 L/R. And in order to hear a played track from Reaper, I have make sure Mix1 L/R is set in the master output. i would think it should be Mix4 L/R.