After consulting a couple of experts I'm confident the Appliance has to be seen as "mere aggregation" of a shareware component with GPL'ed software corresponding to §2 of the GPL. To make this more clear I have made some changes to the current appliance: My own GPL'ed component YAFPC is not compiled into the appliance package any more; The preinstallation of the appliance was replaced by an installation script, thus the user must conform the installation first; And all GPL'ed software have been made public (incl. sources) on a new project homepage as "General-Purpose Appliance System" to be useable for other software appliances too.
Hope that nobody bothers me again with accusations about violating other licenses.
Have fun with YAFPC-Appliance!
W.U.