Boot an Ubuntu ISO via iPXE

[obie]

So I'm trying to make an iPXE USB image that loads an Ubuntu ISO hosted on an HTTPS url that loads that OS onto a Legacy BIOS System.

I've previously gotten an iPXE image working on USB that loads CENTOS kernel and initrd images. Now I'm trying to boot an Ubuntu ISO that has custom binaries and files that I've made.

There seem to be a good amount of posts on the forum about booting an ISO for example:
http://forum.ipxe.org/showthread.php?tid...t=boot+iso
http://forum.ipxe.org/showthread.php?tid=3728
http://forum.ipxe.org/showthread.php?tid...t=boot+iso

Some using sanboot successfully and some answers where it's 'don't try to boot an iso with ipxe'. I'm still struggling to understand what's the best iPXE way to load a custom Ubuntu OS?

Would sanbooting an Ubuntu ISO just work? Some answers mention using 'memdisk' which I can only find docs for here: http://ipxe.org/appnote/memtest ?
What's the better way to load a custom OS if not trying to load an ISO?

Thanks so much for your help.