Systems vary for what they charge for having both services on separate devices. If you purchase your own SB6120 then you should only pay for eMTA rental. The only issue with that is you have to split your RF for both instead of using one device. I know Arris makes a DOCSIS 3 compliant eMTA. Think it's their 702 model, don't know if your system is or will be using them. Ask if they are going to use or have a DOCSIS 3 eMTA.