For those of you reading this thread, note that it is much easier (and most likely cheaper) to get a hackable Series 2 DirecTiVo than to try and do a PROM mod to an R10. DVRupgrade still sells refurbished Philips DSR704 units.

TechLore Blog

HR10-250, Samsung SIR-S4120R, SIR-S4080R, 2 Philips DSR704s (one connected to a Slingbox A/V). One box used the "Zipper"; rest used PTVnet to enable networking features.