So I want to know how I can finish multichannel(>2) output through WASAPI?
If WASAPI is not ok, how i can use ASIO? I saw somewhere else that i need a portaudio_x64.dll file to suport ASIO, and i wonder if it’s ok for psychtoolbox of any version or the version before 3.0.14 if i have such a dll file?
Also, is there place i can download such a dll file
You can’t, if WASAPI apparently does not expose it.
One solution might be to switch to Linux, as there are reports on the internet of your Steinberg UR824 working, when configured to use USB audio class compliant mode (CC Mode).
If you want to stick to Windows, you need to get a portaudio_x64.dll with ASIO support from somewhere. PsychPortAudio exposes any sound backend it finds in that dll, so if the dll has ASIO support, PsychPortAudio('GetDevices') should also list ASIO devices for manual selection and basic use. Not the convenience bells & whistles we had in the past though, only basics.
Not that I’d know of. You could compile it yourself from the Portaudio source code with the “free for certain use cases” Microsoft MSVC community edition, and then probably use it in-house. Any kind of redistribution would require entering a written license agreement with Steinberg Media Technologies and and abiding by their onerous license and trademark compliance and documentation rules - or risk getting sued by them into oblivion.