To answer Daniel's question, services are stored in the Registry. Go to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SilverAppServerService3.7
(The last character may be 0 instead of 7 if you have SS 3.1)
The ImagePath value tells Windows what program to use. Try putting the +classic switch at the end of the command line like you would for a regular shortcut, and it should work.
An unrelated service that had a command line switch in this location also had full quotes around the path, and had the switch outside of those quotes.