John, you do not need a PBX if you are planning to sell VOIP services. Calls will come in trought the E1,get into the Quintum and go out to the other end via ethernet packages coming out trought the data conection,
On calls from the internt to your PSTN, will follow the revers path.
Your PABX port is used only when you have a business and have a lot of phones attached to the PBX. A suser will pick up the phone and dial long distance 9or international). The PBX will sned the call to the PSTN TROUGHT the Quintum. Except on the cases where the Quintum could save money by routing the calls over the internet.
In you case you do not need to worry about the PBX port,unlees you want to attach phones to the Quintum (something like a call center, or call kiosk of same sort)
In that case you will need a channel bank to convert your phones to the E1 format, to connect to the port on the Tenor.
If you have more troubles, just post again.