I've just found another branded adaptor that seems to work in allowing SATA discs to be connected to a Tivo's IDE cable.
It is branded Lycom and is model ST-106-2. It looks exactly like the Startech one however my eyesight wasn't good enough to read if it used the same Marvell
chipset - the writing was about a tenth of a millimetre high.
Has been chugging away in my Dev Tivo now for 2 days attached to a 500GB 2.5" Samsung HM500JI. Also used it to build the image on a PC.