You need a hybrid optical/copper HDMI cable for runs that long. I use Ruipro for a 35' run. They are directional as the converters are opposite at either end. I strongly recommend that you use a
voltage inserter to power it as the power draw is above HDMI spec. Ruipro pioneered this, and have a good track record. They are not inexpensive.
Make sure you run the cable in conduit. You don't want to damage it, and you want to make replacement easy. There are active devices both ends of the cable, so they could fail. Mine has been running for two years now without problems. For 2.1 you really should be using a powered or hybrid cable for runs over 12'.
Lastly TVs over fireplaces are not recommended, due to heat issues and the TV being much higher than comfortable.