I'm a bit confused... Lets review the sequence of events.

1) you have an electrical problem, and you describe the symptoms
2) MB DOC points out that all the items that are malfunctioning are controlled by the combination control module. You check what you think are the fuses to the control unit and they appear to be OK - so I guess you conclude that the module is OK.
3) But your problem persists so...you head over to BenzWhirled for more advise and opinions.
4) People over there tell you the problem is in the "PSE unit" - first they postulate that corrosion on the terminals is the problem. I'm not sure if the "PSE unit" unit is the same thing as the "combination control module". Is it?
5) You find the PSE unit and clean the terminals - problem still exists
6) You replace the PSE module (at a cost of $390) - problem still exists
7) You return here and inform the Mercedsshop community that "you got a lot more help at BenzWhilred then you did here" and "they seem to be a mechanically minded group"....
8) You then state that "you had a problem of "it not working after I turned the ignition off".. and your "fix" to this problem is to install a master battery knife-blade cutoff switch? How did "it" work when the power was disconnected?
9) You finally managed to fix your problem by opening the door on your way to work...

You then tell people to not expect much help from these boards and that Mercedes "Machanics" are book smart and you imply that they don't really know what they are doing. You also offer to help via E-mail if anyone has any future problems with the electrical system on their SLK's.

I guess I missed the part where you actually brought your car to a Mercedes Mechanic (dealer or independent?) that had the proper tools to troubleshoot this problem?