It looks like the Harmony has code sets for the HomeWorx PVR but I haven't seen evidence that they have a discrete on/off code, it is unclear there is one (and you would have to find a Harmony remote to learn it from :-).

Sometimes you can fake out a discrete on/off by finding a sequence of button presses that work and building an "Off" macro. For example on many BlueRay players you can hit "Play" instead of Power Toggle to turn the device on discretely. This means that you can create a discrete OFF button by hitting "Play" then pause a bit for it to power up (if off), then hit the Power Toggle button, (though this means your BlueRay will now power cycles if you were sending an off command when it was already off). Not sure if Play or Live might cause the HomeWorx to come out of standby or not, or if you can only come out of standby by hitting the Power Toggle button. But gives you something to experiment with atleast.