Swapping Drivers - Headphones Don't Work

I do a lot of audio cleanup for video in Cubase. Part of the process involves listening to the results across multiple devices. As the finished work is generally seen and heard on small tech (phones, laptops, earbuds, cheap headphones) I like to listen to my work on my basic Mac Pro built-in speakers and cheap headphones. (For the record I use Adam A5X monitors / Scarlett 2i2 and Beyerdynamic DT990s for the main process - the cheap speakers are for reference.)

It is of course easy to swap between drivers within Cubase Pro 12 - I have a choice of my Scarlett 2i2, Built-in Audio (my Mac Pro) and Studio Display Speakers (in the monitor). I can get any of these to work.

However, I cannot get the signal through to my cheap headphones, which I would like to plug in to the small jack on the back of the Mac Pro. The small speakers work fine with the correct driver selected, but the headphones never work.

If, on the other hand, I am in Premiere Pro or in fact any environment away from Cubase, the cheap headphones, plugged into the Mac Pro, work fine. When in Cubase, no matter which driver I select, the headphones won’t get a signal from the Mac Pro output. The Scarlett Jack works fine though.

Any ideas? I really would like to make it as easy as possible to reference my output on as many cheap and small devices as possible. I have a few reference plugins but they just don’t replicate the cheap earbud / headphone experience.