FCPX captions av output

Hi Everyone,
Longtime reader, first time poster. I posted this on the Blackmagic forum, but no replies yet.

I'm looking for a solution with FCPX. I'm currently working on a project where a lot of hours had to be translated. I chose to use captions instead of regular titles as it is easier on the system. (thousands of subtitles)
Is it possible to use the UltraStudio 4K Mini (or anything else) to show the captions in the AV output? My dealer ran a few tests but couldn't figure it out and I can't visit him at the moment.
In the documentation it seems as if SDI output supports captions, but I can't find anything and with the current system I would have to connect through HDMI.
system is:
Mac Pro 2013 10.15.5
FCPX 10.4.8

Any & all help appreciated,
Sandro

Search BHphotovideo.com for USB to SDI converters. They're not cheap, and I don't know if they keep the closed-captioning in the video stream.

Another option is to get an AppleTV, plug it into whatever you're showing this on, and simply use AirPlay with a video player on your Mac (even FCPX with Shift-Cmd-F).

Depends on what you expect.
If you expect "Broadcast" captions in terms of embedded into the signal FCP is the wrong app.
Otherwise use Ben's advice or any monitor which can be addressed as AV device from FCP or any second monitor to view full screen.

I haven't used Apple TV, would seem that there would be a lot of lag. I want to use a third screen full screen with the subtitles visible. Colour accuracy is not a must right now. I can switch the captions to basic titles, but I really like the use of captions.
By the way, thank you Andreas, used your apps a lot a few years back. Right now I'm using a combination of Final SRT, SRT converter, X to CC and a website which converts XML's to SRT. But I learned a lot using your apps & reading your posts (here and on Cow).