Okay Guys, thanks for the confidence :-) but most of all thanks for looking into this.
Here are a couple of pictures, one is taken from the manual of the Sony STR DA 5400 ES http://pdf.crse.com/manuals/3875810111.pdf
, the other one is from an Onkyo TX-STR876 and one from my elder TX-DS939 (The TX-DS939 documentation also mentions Xantech in conjunction with mulitroom).
Also quite often there is a 12V trigger jack, not 100% sure what it's for, but I think you can trigger power up to compatible components such as TV or projector.
There's another related subject I'd like to mention here: Before setting out to buy my first LCD (for LMCE purposes) I did extensive digging into the RS232 capabilities of LCD TV's on the market. I was interested in e.g. Sony Bravia and Phillips because they stood out for picture and color quality. I found that the US high range models of the Sony XBR range differ from their EU couterpart in that the EU models were 98% identical, but they missed the RS232 port. I got in touch with Philips to get some explanation (for the Philips models) and was told that USB was the next generation, and, USB should be capable of handling the same signals as RS232, I also found a specific USB / RS232 converter that might work in this case (I have a link somewhere...) I also found for the Sony counterpart, that "there seems to be a way to control these LCD TV's via USB in "hotel mode"....(No more detail)
This made me think that perhaps it should be possible to transmit RS232 commands over USB or the case being direct over the IR blaster cable connexion...