Can the FireStudio work in standalone mode?
A while ago, I would set-up my MOTU to pass the SPDIF in to my monitors. Then I used a Linux compatibile Soundblaster that had a SPDIF out. So I wasn't listening through the interface per-se, but at least it was all digital. But the MOTU could be run without the computer and pass audio via the internal mixer.
I know that Presonus now has the internal mixer, but I don't know if they will work standalone. Just another option.
Or run them through a monitor controller and switch them.