Turbo Sound Next
From SpecNext Wiki
Turbo Sound Next is the audio system integrated on the Spectrum Next. It features 3 AY-3-8910 sound chips as used in the Spectrum, plus a MOS 6581 (SID) as used on the Commodore 64.
NextPort:$FFFD controls the selected chip and enables and disables stereo channels per chip. NextReg:$08 controls the mapping of chip channels to stereo channels.