Submix effects are multi-channel (in fact they have to support up to 7.1 audio even if the game is connected to stereo). Source effects are currently only mono and stereo! Eventually, I might come up with a way to open up source effects to multi-channel sources, but it’ll probably be when we tackle general/better multi-channel source support (e.g. not requiring splitting multi-channel source into separate files with a naming convention, etc).
These little experiments are great! Keep them coming!