It saddens me that I feel like every interaction with Comcast is a "process" at best and an outer circle of hell on average.

They have a list of approved modems for the both the residential and business services, with the business one being a small subset of the residential one. But I was able to get a modem approved only for the residential service on my business account by calling around. What worked for me after only a few tries was calling into the residential tech support and having them add it. It's apparently all the same infrastructure on the back end.