Can anyone tell me if it is possible to record onto the HDD via this units external inputs (eg from Sky box) or if the HDD can only be used to record from the Sony's own built-in decoders? The Sony techncal spec doesn't make this clear.

I have an RDR-HXD710 (same machine, but with a smaller hard disk and no HDMI).

I have only recorded from an external source on two occasions when I was recording films being broadcast encrypted on TCM, so I was using the DTT output to the 710 via the SCART. On both occasions I recorded direct to DVD, but as far as I'm aware I could have recorded to the hard disk had I selected it.

I have a 710 and regulary record from a Virgin cable box, I cabled the virgin box into the 710 on line 3 and when I wish to record I just change 'input slect' to line 3 via the remote...no problem

You have two external input options: L1 & L2.

L1 refers to the SCART connection on the backside. You can configure this as either RGB, S-Video or Composite.

L2 refers to the video / audio connections on the front side of the machine

I hope my post has been of use

Thanks for your responses .