As far as I've seen, you should set sound to "normal" or "narrow"
Wide kills the L+R level and usually reduces levels on a channel with no L-R stereo separation.
Well, I have to say I'm glad that I'm not the only one having this problem. Seriously, I need to basically jack up the sound on the TV to nearly 75% to be a decent hearing level over the HDMI input.... when my Xbox over HDMI is nearly blaring at 40%. I've been thru all my settings and can't find anything to resolve this....
I've noticed the same thing when using the Xbox TWC app as well.