I have a Tivo XL4, passing through my XB1 to my preamp and from their to my JVC RS1 front projector, which shows in 1080P on a 100" screen.
Before I used the MS supplied cable to connect the XB1 to the AVR, the picture was substantially degraded. I was using a hefty (and pricey) Audioquest HDMI cable. After, it is either only slightly degraded in terms of sharpness, or not degraded at all. Brightness is unaffected. I changed nothing about the display calibration. Overall, I'm perfectly happy to have the image go through my XB1.
Reaching for the Next Level With a Sony 350ES and a 133" 2.35 AT Screen