Hi Robert,
I've been using iPXE with the following entry successfully:
kernel nfs://192.168.8.158/clients/tce/boot/vmlinuz64
initrd nfs://192.168.8.158/clients/tce/boot/corepure64.gz
imgargs vmlinuz64 waitusb=10 nfsmount=192.168.8.158:/clients tce=nfs mydata=pxe lst=pxe.lst host=pc lang=en_GB.utf8
I hope that is of use,
Regards