Internet Speed

From the street to the house to the Xfinity CGM4981COM it is connected via coax. From the Xfinity equipment to my Synology RT2600ac it is connected via CAT6.

Confirming that the CAT6 cable needs to be connected to the red port on the back of the CGM4981COM?

Modem/Gateway is Xfinity CGM4981COM. The router it is connected to via ethernet cable is a Synology RT2600ac which is 2Gpbs capable.

The XB8 has a red port on the back which enables 2.5 gig through put to another hardwired device. You have the Ac router which does not have a 2.5 Gb port, so you cannot get the speeds you seek without updating to the RTX2600ax which does have a 2.5 gig port. A month or so ago switch with 2.5gb capabilities so I could run my hard-wired devices at the higher speeds. A simple google search supplied this.

The Synology RT2600ac has four 1 Gigabit Ethernet LAN ports. It also has one 1 Gigabit Ethernet WAN port. While it doesn't offer 2 Gbps ports, it does offer Gigabit Ethernet connectivity for its LAN and WAN ports. 

The advertising from the Manufacture states "2.5gb throughput" which is the misleading part. It is all in the advertising.

EG - Thank you for your response and information. Based on the information you provided, I did some research and found a way to reposition the router so that the wireless provided the coverage and the PC now has the 2Gbps. Speeds are amazing!