Can I use the CXA61/81 with pre out only to an external amp without speakers connected?

You can use the CXA61/81 pre amp output only, without any speakers connected.
This would mean that you could connect to an external power amp for driving your speakers, with no speakers connected to the CXA61/81.

Please note;
When speakers *are *connected to the CXA61/81, it is not possible to mute them whilst still sending an audio signal via the Pre-out. They run simultaneously. Mute and volume attenuation affect the main speaker output and Pre out in the same way.
This is especially important for those who wish to use a headphone amplifier as you cannot mute the speakers and send an audio signal via the pre-out. It would also be muted.