Sounds like you are getting a bit mixed up.
Firstly any single tuner basically locks itself to the channel it is recording.
The BM7000s did this, it wasn't capable of watching and recording multiple channels.
The terrestrial tuner is in fact a hybrid tuner, which means in theory you can run it off an ordinary Ariel
or you can run a cable line in the box.
The firmware has lagged the release of the box, I believe the BM8000_109P version
now allows you to enter a cable line. I have just put it in the download section
here
This basically makes the box a twin tuner, so you will be able to record on sat
and watch on cable. (or vise versa)
So you need a sat line and a cable line if you want this function.
I haven't got this box so I can't really help with the set up.