He's said he has looked at the manual for it and cant find it,
So therefore if it was a G2, he would of seen the silent part set option, which is the only option to him on a G2 4 wire.
The earlier Accenta's have NO option for a silent part set, The later G3 & G4 range do, and its documented in the manuals
He said that there was nothing in the programming for a silent option, This indicate to me its not a G2 as its covered in programming
Therefore I would assume that must be an older ADE Accenta 6 or 8, or a later Honeywell equivalent G3 or G4 range
Either way, Dropping the Sound wire on an older ADE Accenta version or the later Honeywell G3 or G4 works as I stated above