I'll begin with some generic help, and you let me know if you need more details.
The Mediatrix 41xx series of SIP gateways converts between SIP & analog. So your 4102S will emulate two SIP subscribers (phones) configured on a HG3500 gateway in the V5 4K. The gateway must be configured to support the function "SIP" using AMO BFDAT. After the HG3500 gateway is properly built (AMOs BFDAT, BCSU, CGWB), you'll need to build the two SIP subscribers using AMO SBCSU. This config is different from a HFA subscriber. SIP subscribers also need a parameter set in AMO SDAT -> "MBCHL".
The Mediatrix can be administered using your browser. It may be necessary to use "Unit Manager Network" to perform a backup of the Mediatrix, or to set the hook-switch timer of the analog device, but 99% of your task is done via browser. In addition to the Mediatrix' own IP address, you'll need to configure the Mediatrix to register with/to the IP address of your HG3500 gateway. You will also need to assign the two newly-created SIP subscribers to the Mediatrix. Ultimately, when the Mediatrix boots, it will register both SIP subscribers with your HG3500 gateway. The Mediatrix will provide the dialtone on the two analog devices. When you dial on the analog phone, it will take approximately 5 seconds for the digits to be sent to the HG3500 "enbloc". Then and only then will you know whether your setup is working.
You should be able to tell if the Mediatrix' two SIP subscribers have registered with the HG3500 by accessing the HG3500 gateway via browser. Click "EXPLORERS", then click around until you locate "SIP Clients". You should see the two Mediatrix SIP subscribers listed here as "SIP Clients" IF the Mediatrix has successfully registered them with this HG3500 gateway.
Good luck.