Constant audio issues with MagniFi Mini

I have a Polk MagniFi Mini connected to a Samsung UN43NU7100, watching cable (Comcast) through their XG1v4 4K HD DVR box. Everything's connected via HDMI and HDMI ARC. Sound is great BUT I have had constant audio sync problems from day one: audio lag, audio static and stutter, etc. I have tried optical rather than HDMI cables. I have tried every possible input/output setting on the DVR box and the TV. I never had these problems with my simple little Bose Solo system with an optical cable connection -- inferior sound, but no problems. Any suggestions out there?