You can set the directional buttons to any IR command you like. Go to the Activity options and select Change behavior of buttons. There you can reassign any button (almost) to any command from all of the devices for that activity.

But that begs the question - why do you want to use those buttons and not the volume +/- buttons? Sounds like you're not using activities properly.

Each activity is a unique set of devices and settings/inputs. So if you watch TV with and without the receiver, set up 2 activities - one with the receiver device and one without. Then you tell it you use the receiver for volume control in one activity and the tv volume in the other activity and in both cases the volume buttons will work properly.