using stereo returns as extra inputs

https://www.amazon.com/Mackie-Onyx-1620i-16-channel-Recording/dp/B002M3TQ44

with the Mackie 1620i & MPC 2500 (i have neither, but I'm intrigued by the possibility if the below is possible)

How would you setup a DAW recording (in either Reaper or Ableton) for recording the Mackie Stereo Returns, on to separate audio tracks, as you normally would the inputs on top of the Mackie?
Example:
Stereo Return 1 "L" -> DAW channel 1
Stereo Return 1 "R" -> DAW channel 2
Stereo Return 2 "L" & "R" -> DAW stereo channel, and so on...

The Mackie Onyx 1620i has 4 Stereo Returns, each labeled "L" & "R". I was thinking I could use these returns as inputs for the MPC 2500's assignable outputs, both in combinations of hard panned and stereo outs.

Then I could be left with all the open inputs on top of the mackie for other synths or modules, instead of mpc outs only needing to be tracked.

I feel like there is no way to get separate recordings from the returns at the same time, and instead they would all be playing together, so no real multi-track recording could be possible.

You can try it. I think quality will be lowered a bit.

do you put anything from MPC through your other boxes, as it would be better to use AUX sends and returns for any boxes you have with inputs. . But you can use returns as extra ins no probs, The gain range might be different and you have no EQ

Pro Tip - you could piggy back using an insert IO on the back of that mixer. You plug in synth in 1 an 2, then use insert to go out to MPC and then return the sum of MPC and synth. but that is not good for tracking, just an idea of what you can do as well