You have to mount both C and D drive iso images with the imgmount command. My autoexec section looks like this (Win95 on a 512 MB image, Diablo and MM6 on a 2 GB image, both on external sd card):
imgmount c /storage/0000-0000/Games/PC/Win95/c.img -t hdd -fs fat -size 512,63,32,520
imgmount d /storage/0000-0000/Games/PC/Win95/2GB_MM6_Diablo.img -t hdd -fs fat -size 512,63,64,1023
boot -l c