First of all the test of my last post did not succeed, so still some work to do to enable me to record things when the system is in sleep mode. No time to investigate this further now.
I installed the latest - unofficial - release of the BIOS for my motherboard, hoping that it would resolve the Crossfire problem I encountered. I downloaded the F4D BIOS revision from Anandtech and installed it successfully. Switching the active graphics board to integrated graphics again and re-installed ATI Catalyst drivers (still version 8.3 as I am not aware of any more recent versions). Unfortunately Media Portal is still unstable with this set up. Switching on the TV will result in a crash. So, back to the PCI Express Graphics board.
The weather was nice, so I took my motor bike and got my self a Logitech Harmony 555 remote controller, to enable me to control my HTPC remotely. The Harmony comes with a nice configuration utility, and the utility is even familiar with the Antec Fusion II IR sensor.
I tweaked the power options to keep the system from going to sleep, and scheduled another recording - for testing purposes - during the night. This morning I quickly checked the recording, and it looks fine.