Like src-32, src-16 builds two versions of the boot program for a given card, card.com, for testing with a DOS diskette and card.rom, for burning into an EPROM. Use one of the boot floppy making programs in contrib or make a DOS boot diskette and then overwrite command.com with card.com. Running card.com from autoexec.bat is not guaranteed to work, it may be too late by then if you have started memory managers and stuff which get in the way of the boot. In addition, note that loading DOS at all may interfere with the use of extended memory as DOS may intercept the XMS interrupt so it's best to make a standalone floppy for testing.
Currently only booting tagged images (see documentation) is supported as I don't know when or if Linux/ELKS will support booting off a NFS mounted root. To make a tagged image see the directory netboot-linux.