Thanks for that.

I know the type of converter I have is for using a SATA drive in a PATA system, so that bit of the puzzle is correct.

I also know the drive is communicating to the converter and to a PC fine as I can use the HDD and converter in a conventional PC fine, and can image the hard disk with an OzTiVo image no problems.

I can also read the boot parameters of the hard disk via the bootprom "backdoor" menu via serial (ie the one with the "factory" password prompt) so the TiVo can recognise the hard disk and converter at this low level.

But.... When a conventional boot is tried the hard disk makes initial seek sounds and then halts on the initial bootprom screen and never gets to the first hard disk based splash screen. This is similar to the boot issue caused by dual large Seagate PATA hard disks and I am starting to draw similarities of this to the use of even a single large Seagate SATA hard disk via a converter. What is needed (when I have some spare cash... ha ha...) is to buy a non-Seagate SATA drive and see if it works.