You won't have any sound plugging a multi-slot Neo Geo board into a standard Jamma connector. Only the single slot boards are fully Jamma compliant, all others differ in speaker pinouts (multi-slot boards are stereo, Jamma doesn't support stereo) plus the additional buttons.
All Neo Geo boards will boot on a standard Jamma connector, so if yours is booting to garbage then you likely have a board level problem.
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