On the Speaker cabinet, there are four 1/4" jacks on the side-
Two are labeled PREAMP OUT and the other two are POWER AMP IN.
Plug dummy 1/4" plugs into the two POWER AMP IN jacks and that will kill the signal going to the power amps.
Do not use long cables- they will pickup noise. You can also just plug a short 1/4" cable in between the two POWER AMP IN jacks.
They are both inputs, so hooking them together is no problem.
You can then take the stereo output from the PREAMP OUT jacks to your recording console.
Or, you can plug a set of headphones in the Headphone jack and leave them on the floor next to the piano.