Extra source of SATA-to-IDE adaptors.
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.
6023 - was 40GB - now 250GB and cachecard
6021 - was 40GB - then 120GB and Turbonet - now 250GB still with Turbonet
6020 - was 40GB - for dev work - now 500GB Samsung HM500JI and a TurboNZet