Loading iPXE from RPL

[man-x86]

I'm trying to boot linux, using an old ISA NIC.

Until now, my iPXE setup works with various PCI NICs, mostly Realtek RTL8139s and 3Com 3c905s, either with from their original bootrom or with gPXE/iPXE added to the BIOS ROM.
Chainloading from the original PXE ROM to iPXE and then to Linux, DOS or memtest86 works without any problem.

Now, I replaced the PCI NIC with a NE2000 compatible ISA card (Dlink DE-224 with DE22X4 16KiB bootrom).
Unluckily, the only bootrom available only support RPL and the addressable ROM is too small for etherboot/gPXE/iPXE anyways.

But I discovered rpld, so I installed it on a random machine connected to the same network.

I never managed to boot a recent gPXE or an iPXE image (either rom or pxe images fails to boot or displays "pxe->eb: no pxe stack found!").

Rpld's load/execute addresses are not very clearly explained, but that's only a part of the problem (and doesn't depends on iPXE).
Anyways, I managed to boot an old etherboot 5.4.3 image (works the same way with rom as well as zrom images) from RPL, assuming load=0x1000 and execute=0x1006 (it also works the same way with load=0x2000 and execute=0x2006), following this post.

The RPL ROM loads this etherboot image, then chainloads to iPXE, which displays the menu, load the images and tries to boot from them.
The main problem is to have the PC rebooting as soon as it tries to boot from either memtest, Linux kernel/initrd, DOS floppy image or even memtest86 iso.