I realize this thread is a year old, but I just worked out a solution for this same issue and thought someone else might find this useful. I purchased a Yamaha receiver (RX-V1077) as a replacement for an RX-V1800, and one of the reasons I purchased it was to use the receiver's standby input switching with my Harmony 550 remotes. I have a central home HT equipment stack with 6 HDMI devices that supplies various displays throughout the house, so when in another room I want to be able to switch devices without turning on the receiver - I previously used an external Monoprice HDMI switch for this. I also have wired IR receivers in each room to carry the IR signals back to the equipment stack.
In the Harmony software (V7.7.0 desktop), I added the RX-V1077 as a conventional A/V receiver device, but also added an 'Audio-Video Switch' device under the 'Amplifier' device types. For the manufacturer and model of the switch I used 'Not Listed' and made up a name and model (YamaSwitch, AVSelect) so I was starting from scratch. I said I have a remote for it, and skipped 'Power Toggle', 'Play' and 'Number 1' when prompted to learn those IR commands. I then selected 'Learn New Command' and entered eight commands with the names AV1 through AV7 and AUX, picking up the IR codes head to head for each of the dedicated AV input buttons on the Yamaha remote. When prompted 'Do you want to leave your AV Switch on all the time', I selected 'There are no power buttons on my remote'. For the options to change inputs, I selected Method 2 - dedicated input buttons. When prompted, I then added eight source inputs, also named AV1 through AV7 and AUX. The next dialog prompts for the remote button to use for each input, and I mapped input AV1 to the learned button AV1, AV2 to AV2, etc. and saved the device.
Then I simply added the pseudo-switch device to each of the activities where I wanted to change the HDMI input without powering up the receiver, and set the appropriate 'switch' input for that activity. For the HT room activities, I used the RX-V1077 receiver device instead of the pseudo-switch, as for those activities I did want to power up the receiver. Works perfectly!