Voicefile generation fails on Mac OS Senoma with system engine

[Mudb0y]

I'm a blind Rockbox user, and just bought my self a modded Ipod Video recently. Whenever I try to install the Rockbox voicefiles using the Mac OS system engine with my preferred TTS settings, the generation simply fails with "Could not convert intermediate file."
This also means generating talk files fails, so I have to listen to my files being spelled by the extremely slow pregenerated Espeak voicefiles from the daily builds.
As an aside I also tested with the espeak binary from Homebrew, not espeak-ng, and it works, but I'd prefer to use the Mac OS engine if there's a fix for this issue.