You sure can. I have an ARRIS SB8200 for gigabit, as you do, but I also have an older ARRIS TM722G that was activated as a voice only modem. Works very well in my current Quad Play setup.
Hi, brandonmerc! Glad to hear that you were able to activate a modem and eMTA on your account. However, I just want to add - it's not available in all markets. In some markets, customers can only have one modem or eMTA.