The DVD2 cannot be in the TV, I think, as you would not be able to access the disc tray.
The advantage of the DVD2 is that you can burn a DVD with what you have recorded. You cannot do this with you 2 other HDs.
With the HD in your cable box, the good thing is that it records the digital data without converting it to analog and then back to digital, like HDR2 and DVD2 do.
I would use the HD of my cable box in priority, as you will not lose in quality from the original broadcast.
I would use the HD of the DVD2 when you want to record analog TV, or an external video camera, or when I intent to save the content on a DVD for long term storage.
You may be able to order the BV9 without a HDR...
The DVD2 is looking very nice, and is relatively cheap for a beo product. I am really waiting for its release beginning of september... this is my next beo purchase... and then a Beo5!