The early versions of Hicom 300 (9006 in the US?) used ZAND:ALLDATA params MELODY and HOLDTN to set silence, an announcement, a stored jingle, or CD music, all as a system wide MOH.
If you wanted announcement ("Please Hold The Line"), you set HOLDTN in Zand Alldata to RA. If you wanted the stored jingle, you set HOLDTN to MUSIC and also in Zand Alldata you set MELODY to 1 or 2, depending on which really bad tune you wanted. If you wanted silence, HOLDTN was still MUSIC but you set MELODY to 3, which was actually silence.
If you wanted CD music/IPOD etc.. you also added in SSC an EXTANN (external announcement) port on an SLMA pen, and connected your music device to that.
After changing the above parameters it is usually necessary to activate the SIU with ACT-USSU:SIU,1; dial tone will be lost for a few seconds but no system restart is required.
In the newer UV software, SBCSU as discussed has the additional parameter HMUSIC, where you could also set as a hold source an RCSU HMUSIC port. Adding HMUSIC allows you to override the system wide config with per extn configuration. There is no reason why you can't add a "silent" source to an HMUSIC port and set that against an extension although you must have something connected to answer the ringing signal from the Hipath. If you dont, it will show defective in SDSU and extns that should use that port for MOH will default to the system wide MOH.
Hope that helps.