Signal strength to Tivo Edge DVR

My internet modem is not routinely delivering sufficient coverage for the Tivo Edge DVR connected to my TV.  Tivo says this is caused by low signal strength.  I'm using an Xfinity Modem XB6-T modem provided by Comcast which is in a different room from where my TV is located.  Do I need an signal extender to address this issue? If so, what works with the modem I have?  My internet speed is 600 mbps which is supposed to be sufficient for my wifi devices [Ecobee thermostat, 2 Ooma phones, a laptop, a tablet [usually not connected to wifi], Wemo hall light, HP wireless printer [turned off when not printing]  and 2 Samsung phones. Comcast says I'm getting a good signal, Tivo says it is not sufficient to operate the Edge DVR without disruption.  When my signal strength falls to 50%,  I get a message saying Tivo Service Unavailable and nothing is recorded.