GLT,
I note your statement about requiring using the USB port as a Deep Standby Indicator
At first I used an indicator light on my BT Broadband Ethernet extender to indicate a deep standby condition. That is connected to a 'port' as far as I am concerned.
At this point, I carried out another experiment which involved powering off the Aura at the Mains:
1. I put the Aura into Deep Standby mode;
2. I waited until the HDD stopped spinning and my BT Ethernet Extender LED switched off;
3. I switched off the mains power at the mains socket;
4. I left the power off for 15 minutes, assuming that any energy-storage devices within the Aura would discharge after that duration.
5. I switched on the mains power at the same time as starting the stopwatch.
6. My results are:
a. Time to HUMAX splash screen: 9.0s (it was earlier but I was expecting it to be later so did not react immediately)
Notes: The Aura LED changed to Blue.
b. Time to Active Standby: 1m 14.8s as indicated by the Aura LED turning Red.
Notes: I then pressed the Power Button on the Remote.
c. Time to Live TV: 1m 20.28s.
As this was the first time I carried out the experiment it may be that the times are bigger than in reality because I did not know what was going to happen.
However, these times are commensurate with those I previously reported.
I will seek an indicator of USB power to pursue your mode of indicating Deep Standby.