How can I select specific output channels?

FMOD Engine
6

YES!
Even though it’s not that ideal as you said and not sure if this will always work,
but along with your kind answer, below code works too:
FMOD_System_SetSoftwareFormat(g_System, 44100, FMOD_SPEAKERMODE_RAW, 8);
mySpeakerList[] = { FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, (FMOD_SPEAKER)0, (FMOD_SPEAKER)1};

Or:
FMOD_System_SetSoftwareFormat(g_System, 44100, FMOD_SPEAKERMODE_RAW, 6);
mySpeakerList[] = { FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, FMOD_SPEAKER_MAX, (FMOD_SPEAKER)0, (FMOD_SPEAKER)1};

Thank you!