You’re going to need to review the threads here on using gPXE and interpret them to apply to proxy-dhcp/ltsp/dnsmasq. It should not be that difficult, you’re just going to hand off from pxe to gPXE, then grab the correct menu and go from there. The only difference may be the location of your pxelinux.0 file and the pxelinux.cfg directory location.