Nope, definitely not stupid, I'm just not too good at using words in descriptive format. I haven't had a chance to take or post pics and scanning won't work, other than for the solder-side.
Loosely translated, The SCSI-AUDIO Card adapts the half height cartridge mechanism's raw signal and control lines to something a Mac can use: SCSI!
It's a VERY interesting board and I'll have a chance to document it, and the rest of the CD SC, before I turn it into an ATOMicNetTop. }
edit: it's the "controller board" for the drive you have in the picture!