Sample rates should not be a problem, however making it work with 32-bit audio doesn't seem possible on ffmpeg side. What we need to do here is review our ffmpeg plugin so it properly exports the constraints for each encoder. Right now it pretends to accept any kind of input, but actually doesn't.
Then, it should be possible to configure the dcoders to output matching formats, or insert a format conversion step in the process. But without the ffmpeg plugin advertising its actual capabilities and limitations, this is not really possible.