X1 4k DVR (XG1v4) and Wireless 4k TV Boxes (Xi6) Using a Non-Xfinity Modem

I am currently using a CableCard with TiVo.  I am wanting to switch over to Xfinity boxes to take advantage on the 4k content.  However, I am being told that my desired configuration is not allowable with a personally owned wireless gateway.

I am using the Netgear CM1150V modem, which is Comcast approved for all Xfinity voice packages.

I want the 4k DVR (XG1v4) and two 4k wireless boxes (Xi6).  However, Comcast tells me I am not eligible because I do not use a rented gateway.  It should be noted that I intend to hook up the X1 and satellite boxes all on the same wired network via ethernet connection, so I will not be relying on the wireless gateway's wireless connection for communication.

Does anyone else have this configuration?  If so, can you confirm all works well and they all share the same DVR playlist, etc...?

Thank you.