I notice that the table TBL_MENUCONFIG in setup.db contains a field called HDMI_CEC, but there is no menu option relating to this in the GUI. Has anyone done any experimenting with this setting? My TV can control all the functions of the Blu-Ray player using HDMI CEC which means that I don't need the blu-ray's remote at all. Being able to control the Humax in this way would eliminate (or at least significantly reduce) the need for another remote cluttering up the sofa. I know the Humax remote can be programmed to control the TV, but it just doesn't cover enough of the functions I need. I'm guessing it's something that Humax started implementing but had problems with it. What's the easiest way to modify these databases? It would be interesting to try this out.
It is possible to view databases from the Web-IF from Main Screen >> SQLite 3 DataBase Dump, They can be edited using SQLite Brouser download LINK HERE, It is probably worth saying caution should be used when fiddling with datbases
Has anyone done any experimentation with this? For me the lack of CEC is a major source of (perhaps irrational!) annoyance. Eventually I would like to get power on/off, input switching and volume control working using the Humax remote (or even a smartphone, but that's another story...).

I would be surprised if merely changing a field in the DB would magically get it working, but if Humax have considered this as a possibility then it seems a reasonable assumption that the hardware connections are there. Since I had been considering going down the USB CEC adapter route (http://www.pulse-eight.com/store/products/104-usb-hdmi-cec-adapter.aspx) with libcec, this could be a step forward. The devs have said that they are working on supporting native CEC for the Raspberry Pi in libcec, so if the hardware can be figured out (does anyone know what chip is used?) perhaps the same could be done for the Humax.

The other part will be to interface with the remote keypresses and system state, but can I assume solutions exist for similar things to this already?

Any thoughts on these approaches?
The thought I have is that the HDMI interface is more than likely implemented as part of the system-on-a-chip that underlies most if the functionality, so rather than asking what chip you would need to ask what LSI macro library. That does not make things impenetrable necessarily, the same library might well be used to make stand-alone HDMI chips.
Well I was assuming it would be part of the SoC, which I believe is a Broadcom BCM7405. The Pi is a Broadcom BCM2835, but as you say the interface might well be compatible.

However this post seems to suggest there is a more complex path for the HDMI signal in the Humax (I guess due to upscaling or something like that). Hopefully the CEC signal would be maintained end-to-end, but it could turn out to be a problem. On the other hand it could give multiple options for where to inject the CEC signals. As yet, the ongoing work by the libcec guys for the Broadcom in the Pi seems to make it the best bet.

The truth is from now I'm a bit stuck on where to find the relevant information about the devices and libraries.
I don't know if anyone else has tried this yet, but having sussed out running sqlite3 from the command line, I had a quick tinker with this HDMI_CEC setting, changing the value from 1 (default) to 0 and 2, but it didn't seem to have any effect at all after a power-cycle each time. There's obviously more to it under the covers than just this setting. My money is on the theory that Humax had trouble with it during development and so abandoned it. They probably figured that getting things like iPlayer and YouTube working in the portal would help them sell more units so gave them a higher priority.