I would not use DIR if there’s already a THRU machine (volume doubling and phase issues, if you dont have delay compensation active in the OT’s setup).

About feedback…do you plan to process tracks of OT going back to OT itself?
This case you would have feedback in your routing.
OT’s tracks that go to mixer then back to OT for processing…since, on OT, it’s the same physical output.
****using AuxSend you can modulate a bit of feedback also…this is really awesome, especially if you have two pairs of OT’s fx in chain (Thru+Neibor)

Anyway…
You can use the CUE out for the OT’s tracks that you want to be processed by it.
in Studio Mode configuration.
Just be aware to DO*NOT send to Cue also the Fx processor tracks (feedback!)
So…

1• MAIN OT’s Outs to Mixer, say ch.1-2 going to MixerStereoOut (NO BUS ASSIGNMENT !!);

2• CUE outs to ch.3-4 going only to Bus 1-2 OR use AuxSend (FxSend in your Mackie?) in this case… NO MixerStereoOut
(bus 1-2/or/aux 1-2 > OT inp A-B);

3• all the other synths-----to respective mixer channels and Bus assignments for processing + sampling (Bus 3-4)

Regarding point#2 it’s up to you…this way you can use a Mixer’s channel strips to Eq, amplify to saturate etc…prior to go in Thru machines/Neibor (on track 7/8?) and you choose the SEND amount from CUE Level.