"The Linux one" (Loader2) can load Rockbox. You need a quite recent version and maybe need to configure it a bit. Loader2 isn't our software so we do not support it. Find the information at the IPL pages (but we have a discussion about Loader2 in the New Ports forums).
There is also an undocumented way of booting IPL using the Rockbox bootloader, but this doesn't provide a menu ...