On SX160IS (the only pre-digic 6 camera I have with HDMI), Enable and Disable work as expected in both playback and rec, 4.95V when on.
Interesting…
My sx230 has also 5V in both playback and rec. If a camera has 5V on the HDMI port during playback and recording, why should Canon then install a switch off?
What can the 5V voltage drive? At 1K ohms the voltage breaks down to 2V.
It is interesting in the G1x: If I put the hotplug detect with a 1K ohm to the 4.5V, then the voltage goes to 5V.
I don’t not know if what that means:
My cameras have 8 bytes (?) Between the addresses of EnableHDMIPower and DiableHDMIPower. With your SX160IS 24 bytes.
To be quite sure, I will order once the proposed HDMI adapter…
Minimal HDMI remote for testing 
1 micro or mini HDMI to standard HDMI adapter
1 HDMI standard to DVI female adapter
1 paper clip
If I watch to the picture, I looks like you measure between pin 14 and 16 (+5V and Hot plug detect)