Problem solved. I was missing the BIOS files.

No. Once I unzip the file, I get an .iso, 35 .wav files and then a .cue file.

First off, let me just say thanks and well done. This is an awesome project. When downloading the roms from planetemu for SegaCD as recommended in the segacd rom folder, I can't get them to work. The forums all talk about needing to use bin/cue but the roms downloaded from planetemu aren't that format. I'm using a mac to do all this, but don't know if that's the issue and have been transferring them to recalbox through finder over the network. Is there something I need to do to convert them? Any thoughts?