just tried yesterday. Plugged in an additional power supply, then deactivated internal bluetooth, deinstalled bluetooth, plugged in external adapter, installed bluetooth again. M2P sees my smartphone, but not the other way arround. Pairing not possible. The same with Echo dot. So reversed the whole thing and got internal bluetooth up again, but even with 2 power suplies the problem persists. Pffff…… Tried to not stream to LMS server, but instead to audioplayer. In advanced settings I selected pulse, but with this configuration no sound is comming out of AMP+, which I already expected.
Will try a different PI(Model B) today to see, if streaming might work on that one.