Yes...the DIUT2 is the S2 (ISDN Primary Rate Access PRA) Module used to connect with an S2M ISDN PRA (Primary Rate Module, 30 B Channels + 2 D Signalling Channels) and not for S0 ISDN BRA (Basic Rate Access, 2 B Channels + 1 D Signalling Channel) provided by STMD3.
You can't connect a ISDN BRA to the DIUT2 Module's interfaces (and vice-versa).
Did you have two Trunks Boards?
Did you have a DIUT2 Module (2 ports 15 pin Sub-D jacks) and an STMD3 Module (8 ports RJ45) both installed inside the same HiPath 3800?
Basically this is not so strange (it depends on your PSTN requirements, BRA/PRA) but you should then pay attention: S2M ISDN PRA is definitely NOT S0 ISDN BRA...yet at first sighy they have very different ISDN Network Terminators.
Regarding the optiPoint 500 Advance (The UP0/E interface needs only a very normal telephone cable with two wires connected centrally on a RJ11 connector): you need to connect the optiPoint 500 Advance to the first (for enabling Management from the phone, if you want) port of an SLMO8 Module (the one with 8 UP0/E interfaces) or SLMO2 Module (the one with 24 UP0/E interfaces) via RJ45 Jacks.
The phone will then power up automatically (it will show you the Extension Number you programmed for it or the default one based on the system port you connected it) and you should see it through the HiPath 3000/5000 Manager E (once you read the KDS).
Best regards, Kimera.