Hi, to my knowledge there is no way around in your case. The only way to get 5.1 is to get a source directly connected to your 5.1 system with Hdmi image pass through (Quite common) to the ppmax.
5.1 surround systems existed way before HDMI, Bluetooth, and digital audio connections. It’s all a matter of how it’s encoded into the stereo signal output by the PPM.
If you can find a Usb sound card with 5.1 support on android, please try it. I think we tested a few but don’t remember the result. @Philips_Support_N ?