Here is a diagram of the Heating/Climate Control system and the tempreature sensors. I doubt this will help much though, other than seeing where the floor vent register is. I am guessing you've discovered that already. Why not take it to the dealer and complain? You're a doctor for God's sake! You don't have time to troubleshoot this stuff!
BTW, this image is from the Porsche
Service Information Technik for the 2004 Cayenne. It can be ordered from your dealer, part # PNA 488 910, for about $63. It is an excellent overview of the Cayenne designed for the Porsche technician.