5.1 & 7.1 mixdown and stereo monitoring

[cameron-fmod]

Here is some additional information on downmixing:

Surround to Stereo Downmixing in v2.02: discrepancies between auditioning stereo in Studio vs in Engine

SRS is no longer available in FMOD, we replaced it with a Dolby PL2 downmix, however that downmix is opt-in via FMOD_INIT_PREFER_DOLBY_DOWNMIX. The default downmix is a simple mix matrix performed by either the Core API or the Studio API. When the master bus is set to 5.1 and the output device is stereo, the Core API performs a downmix like this: { 1, 0, 0.707, 0, 0.707, 0 } { 0, 1, 0.707, 0, 0, 0.707 } When a Studio bus takes 5.1 input and is forced to stereo output the Studio API performs a…