the problem is where do you get the CPU dump from, once you removed from the snesdsp bios? fullpath loading does not handle multi files (see e.g. scv carts with multiple roms which cannot be loaded from fullpath), it just loads the first file it finds.
so even if you don't need the xml strictly speaking, you still need rpk to handle multifiles to get not only the cart rom, but also the DSP rom from the zip archive