Forcing transcoding for FLAC files

I have a lot of music files as 16/44k FLACs. Serviio serves them up nicely to the devices in my home that support FLAC, and for the rest, I have setup device-specific profiles that transcode the FLACs to MP3s. All good. But I have one device that claims to support FLAC, but its implementation is buggy. For this box I would like to force the transcoding of FLAC to MP3 even though the box tells Serviio that it can handle FLAC. I tried a variety of profile tweaks, but it appears to me that Serviio believes the box' claim of FLAC support and sends the original FLAC every time. What's the XML for "Don't listen to the box!"
Thanks for any advice.
