Choose the option on the Sony that offers the lowest sby power. It's a EU power saving requirement for newer kit that the box should be capable of a sby power consumption of 0.5W and still be able to record.
Hmmmm. Oooh we mustn't upset the EU, must we.
More seriously, why would I want to change anything about an old Sony device that is working well just to save a tiny bit of power? There's an awful lot of nonsense about this sort of thing. Here the house thermostat is in the lounge, the TV based electronics is in the lounge, so for about 97% of the year here in the North, a little steady 30 watts probably holds the boiler off for the rest of the house for a decent time each day.
Many thanks for the replies, though. I now understand that the Humax does have a long start time, and so mine probably isn't faulty.
Everything else seems so far to be fine, although I'm still amazed that the original design seemed to have no aerial pass through before the software update and has an indicator that looks the same to say "OFF" or "Recording".