Hope this is the correct place as I don't need help..just informing...
I compiled the newest git for this core on PC/64-bit and RaspPi3...and chd support works well as far as I can tell.
Sonic CD as bin/cue is 573.5MB and the chd is 317.8MB. I see this as a good thing for the PI as a 128/512GB card is still a wee bit on the pricey side..and forget about a 1/2TB card! 0.o Yes a hard drive is cheap even with a powered usb hub..but less heat and wires :D
Remember you'll have to update your es_system.cfg so that emulation station will add the new extension! Happy gaming! :D
(the wiki needs to be updated to reflect this now..and super-grafx (tg-16CD is chd as well..)