My own little PEBCAK:
Burned a bootable micro-sd card for ver 8.0 X86 with CorePlus and used the USB-HDD option checkbox.
I got over-zealous and dutifully added waitusb=10 to the custom boot option line. Not necessary, but thought so since I was essentially doing a usb boot.
When I checked my bootline at
/mnt/sdb1/boot/extlinux/extlinux.conf
I noticed there were TWO instances of waitusb - mine and the installer's.
I removed my redundant waitusb option, and just left the installer's own waitusb=5 that appeared before the UUID's.
I guess I like things tidy.