Harmony One - Custom Actions
I posted a query a few months back about whether you could add extra commands to an activity (eg. set the sound mode on an av amp to source direct when listening to CDs) but have only just found out how.
You can do it via Custom Actions which allows you to add ANY command to an activity, but so far I've only been able to access them by adding a device to an activity after selecting the 'add device/specify further options' option.
If you don't add a new device then the custom options page isn't shown, which sucks.