I have never been able to get sound from the QB64 to the rear speakers, but it is possible that I will have a mistake because the rear speakers usually play very quietly. In your program, I rotate the mouse sound left, center, and then right. The front / rear doesn't work, but as I say, it wants someone else to try it as well. I have Logitech 5.1 speakers and it also depends a lot on whether I have a dolby digital switch and a switch on the speaker driver. When I switch that switch, my subwoofer gains and weakens when I move the mouse in the Y axis, but the rear speakers still nothing.
So - please test it also someone else with 4.0 / 4.1 / 5.1 / 7.1 speakers
I would also be interested in someone else's result.