lol i just tried it and it worked it actually says
The Record outputs on Cambridge Audio AV Recievers will only output a
signal in the same format it is recieved in. If an input is digital
(optical or coaxial), this will only be outputted by the digital
outputs, and if a source is analogue, this will only be outputted from
the analogue outputs.
On the 640R, the signal sent to the REC 2 output must be selected in the On Screen Display.
The Pre-outputs will output whichever source is currently selected, irrespective of whether this is analogue or digital.
on the website lol, btw if i turned the receiver volume right down so that the speakers wernt audible, i should then be able to amplify the signal to audible levels with the external headamp shouldnt i