I know this is an old question, but I am currently working on a fully implemented layout of the Roland D50. This is the main reason i bought MidiDesigner in the first place. I just finished the first page (Upper common) after about 7 hours ;) , and I'll be working on it as time permits. As the controls of the D50 are a bit confusing, i'm adding the right labels where necessary (taken from the manual) such as with the PCM sample names, EQ frequencies etcetera.
I was already helped with a problem earlier today after only minutes, so i am confident i will be able to get this to work fully and completely. It's a shame the D50's controls are so terrible, because it has a lot of potential.
I'll share it as soon as I am ready!