I discovered today, there are 2 harmony skills you must enable to be able to do anything other than turn on/off your AV items... The "blue green" one sets up the equipment by making each activity a "device" to Alexa... the second gives you control over the bits while you have things turned on or off or whatever as long as the Hub was the last thing to communicate with the AV system... Thus allowing all of the volume controls and such by voice... If you only enable the red skill... everything requires "Alexa, Tell Harmony to _______.".... The Blue green one allows you to Tell Alexa directly... "Alexa, Turn on TV"... or "Alexa, Turn on a Movie" Once the movie or TV is on, you have to tell Alexa to tell Harmony to do things, such as change channels, or Turn up volume... I understand it's also supposed to control FF and Pause and Play too... haven't had time to give those a shot...
Hope this is helpful to some who are just getting into this and things are slowly making sense.
Something else I noticed about the Harmony set up, is the account linking bit is not straight forward... It gives you screens to walk through, but doesn't explain them well, and sneaks the "Link to ____ account button as a bar across the entire bottom of the PC screen if you're using a computer for set up and configuration of skills and such... I nearly never figured that out as I wasn't looking at the bottom of the screen and just kept flipping back and forth from one to another trying to figure out if I had linked accounts or not... This may look more normal on a Smart Phone... but threw me for a loop for a while trying to figure out why my account wasn't linking...
Again... The Blue Green Skill allows
"Alexa, Turn on a movie."
The Red Skill Allows Controls of those AV Components
"Alexa, Tell Harmony to turn up the volume" (which it does on my amp, in 3 notches at a time when asked)
I cannot tell you if anything else specific works, just the volume so far... everyone went to bed and asked me to keep it down for tonight. I'll try some more items tomorrow.