Just received a Tvonics MDR-252 STB of which there seems to be plenty on Fleabay at reasonable prices.
Positive points:-
Very small - only 200 x 90 x 30 mm
Although the included wall wart is rated at 5.1v it seems to run quite happily off 5v (>1A) so should have no problem running off the Tivo PSU.
The 'Auto Standby' feature can be disabled.
It comes back in the 'on' state after a power cut although it does default to channel 1 (not a big problem).
So, just need to collect the IR codes and I should be in business Gonna be much easier to integrate internally then the Sony.
R.