If you've already compiled your own iPXE, you can load up the netboot.xyz menu easily by entering CTRL-B when prompted setting DHCP and then chainloading iPXE:
dhcp
chain --autofree https://boot.netboot.xyz
If you don't have DHCP on your network, you can manually set your network information:
set net0/ip <ip>
set net0/netmask <netmask>
set net0/gateway <gateway>
set dns <nameserver>
ifopen net0
chain --autofree https://boot.netboot.xyz