Multi output predicament

In Cubase /Nuendo I can import mastered Stems from a previous cue, and output them on Stereo output 3-4

I can write new stuff and output it on sterero output 1-2 where I will apply some mastering plugins without affecting my already masters Stems ( on steroids out 3-4 )

I can hear both outputs in the same time. No problem.

In Logic I have to chose to monitor 1-2 OR 3-4.

I tried messing with the virtual Chanels of the Apollo with no success

What am missing please ?

Thanks

Inputs and Output channels in Logic are tied to their respective input and output numbers on the connected hardware audio interface. So whatever you're routing to Outputs 1-2 comes out of the Outputs 1-2 on your interface, whatever you're routing to Outputs 3-4 comes out of the Outputs 3-4. If you don't have any speakers connected to Outputs 3-4 then you won't hear anything routed to Outputs 3-4 in Logic.

An alternative is to mix to a bus: set the output of all your channel strips in your Mixer to a bus, set up two Aux channel strips with their inputs set to that bus, and set their output to Stereo Out.