ALTERNATIVES WITH MULTIPLE OUTPUTS TO BLACKHOLE FOR APPLE M1?

[NewFutureFantasy]

On my Apple M1 Mini, when I run Ableton and choose my Saffire 18i20 as the output, I can have the metronome on output 3-4 for just my own monitoring while the main output 1-2 does not broadcast the metronome to the listener, ideal for an acoustic song where I need precise timing but do not want any percussion.
However, to live stream using OBS I route my audio via BlackHole. I create a multi-output device in the Apple Audio-Midi Setup which has both BlackHole 16ch and Saffire18i20 as outputs and set this multi-output device as the output of Ableton, with OBS taking audio straight from BlackHole 16ch. But then I only have outputs 1-2 available on Ableton and there is no output 3-4 available to monitor the metronome without the listener hearing it. Perhaps this is because the Multi-Output Device that Apple automatically creates is 0in 2out, despite BlackHole apparently being 16ch.
Is there a way I can monitor my metronome on a separate output while live-streaming via OBS, perhaps with BlackHole or maybe an alternative, that will of course work with my M1 chip? I have searched the internet for an answer but to no avail.
Many thanks.

[Etienne1973]

Create an Aggregate Device in Apple's Audio MIDI Setup by coupling your Saffire interface + Blackhole 2ch together. Choose this Aggregate Device as input and output in your Ableton Live audio settings. Make sure you mirror Saffire output signal 1-2 to Blackhole 1-2 output in Ableton Live. Last step: In OBS choose Blackhole 1-2 as audio input.

[NewFutureFantasy]

Thanks for you suggestion. I did create an Aggregate Device containing both the Saffire and BlackHole. Ableton saw this fine, but the Audio Output Device in OBS can only see BlackHole, which is now not sending any audio, unlike when I used the Multi Output Device, when again OBS could only see BlackHole but it was delivering audio. What am I doing wrong?
I am not sure how to mirror the Saffire output to BlackHole output in Ableton Live.

[Etienne1973]

I can't tell you how that's been done in Live. But does this video (above) help?

I am not sure how to mirror the Saffire output to BlackHole output in Ableton Live.

[vurt]

in obs, which audio in are you using?
there's a few options like inputs 1/2 or desktop audio and so on...

i use desktop audio, then use my scarlett mixing console, to route the various things around.

don't know if this will help, im on windows so don't know if it's different.

[fhunktion]

Audio hijack pro is the way to go. You can choose to send individual apps to a specific out put or all system audio. Still need to set up the aggregate device but it's makes it easy to switch what audio stream is being sent where

[guitarplayr82]

Check out the app LadioCast. If you use it creatively with BlackHole it might be able to solve your problems and it's free.

[Funky40]

there is also "Loopback". Also from rogue amoeba.
But seems that "Audio Hijack" just recently got some features from "Loopback" added to it.