Philipp> Apparently none of the common key-combinations work for entering OFW..
Philipp> SysDisk doesnt work (like FAQ says) and the provided Boot Variables
Philipp> wont work, too.. :(

Which you mean by this phrase
 (1) You do have serial console runs 38.4k and connected 
     to the StarMax modem port and  pressing CMD + OPT + O + F
     doesn't bring you to the OF World at power up.
or 
 (2) You hit above combination but nothing happens on the screen ?
 
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Makoto Fujiwara, 
Chiba, Japan, Narita Airport and Disneyland prefecture.