When I first got it and there seemed to be no option in the power settings to leave loop through on in standby, I sent Humax a message, which they've just responded to:
Thank you for contacting Humax Support.Please accept my apologies for the delay in response to your email query, unfortunately we have experienced a large number of contacts which has concluded with a backlog and increased response times.
Unfortunately the loop through feature of the HDR-2000T will only work whenever the unit is switched on and it cannot be operated from standby.
So now I'm thinking I'll have to use a splitter so it can be powered down, or just not use the TV's tuner.