MPC ONE Recording USB audio input/main out in Controller Mod

As the name suggests, I cannot seem to work this out/google a solution. Lots of similar but different issues and topics come up. Is it possible?
If I can in controller mode, then can someone advise how?

So first off I go new project and have track Audio 001 which defaults to Input 1, 2, and I can't change that on the MPC but I can use the software and where I have the options to change from stereo 1, 2 to Mono 1 or 2, but no internal.

My set up is:
e-drums - drumbrain - mpc - (PC: - daw - drum vst - sound out) - mpc - sound system/headphones.

Essentially I want to be able to use the mpc as a glorified audio interface, plus record the main out, to relieve my computer a bit of labour which it's struggling with, and do the recording with the controls/buttons/etc on the mpc so I don't need a mouse, or really touch the computer, whilst drumming.

Seems all the tools are there, just can't seem to make it happen. Thank you!

Well for fear of coming across like I haven't read the manual and getting the tirade of abuse or absolute disregard that that might cause, I have gone and re-read the sampler chapter and some other bits, and sure I forgot it says its possible in controller mode, but still...why isn't it working?

I don't get what I'm missing, followed all steps outlined

Ableton is set to output 1 and 2, the only options using the mpc one as my interface.
MPC to amp, headphones off that so the sound is there and going through the MPC.
Source on the Sampler set to Resample L + R...
It either lets me save samples, and they're just blank wav files, OR on a few of my further attempts I get An "Error Saving Sample" message (drives not full or any rights changed since the blank files were saved).

"Sampler

The Input Source menu in the upper-left corner of the Sampler panel defines whether you are going to record an external audio signal (Stereo or Mono) or an internal signal from within the MPC software (Resample L, Resample R, or Resample L+R)."

Says the manual. "Internal signal", is that actually specifically internally generated sounds? And its impossible to record any audio coming in digitally on the USB, like a backing track to what you're doing on the pads or something?

Seems a bit limiting for the sake of being limiting not being able to reroute stuff like that!?