If you're in an exploratory mood, go to www.getzweb.net/jp1/, and try a Protocol Search, using Denon as the protocol.  Leave percent signs in all the device numbers, and select URC-7800 as the remote.  You'll see that 0004 is Denon, device 12, and 0160 is device 2.  There are 3 other device numbers available in the Cinema 7, so you might try those, perhaps with the power button. 

If that doesn't get a response, try systematically pressing each key on the remote while watching or listening for a response.  Do this for all 5 device numbers, or until you get a response.  If any remote button triggers some kind of action, then we know which device number the PRA-1500 responds to (hopefully only one device number).  At that point we can systematically try all 256 EFC values to find what values control the various functions of the pre-amp.

See www.remotecentral.com/cgi-bin/mboard/rc-remote/thread.cgi for an illustrative explanation and example of how to do this.