The pvr150 won't show up in the connections wizard, just the core, the tv (or other viewing device) and the cable box. Once the video and audio pipes are drawn for the cable box to the core, you should be set. The channel change script is :
and takes the form of :
TuneToChannel.sh <device to be controlled> <Media Room>
For an example if your cable box is device #51 and the viewing area is the first room in your rooms list (mine is the living room) is #1 then the format would be:
/usr/pluto/bin/TuneToChannel.sh 51 1
This is what you would put in mythtv-setup under channel change script.
Hope that helps, I will verify this tonight and post back if there are any changes.