Plug one of the LAN ports into another PC, and run tcpdump on that machine:
# tcpdump -i eth0 -n -s500 -X ip
Then power up the Asus. Do you see a broadcast UDP packet, I think it's to port 4919? If so, press the reset button within 2 seconds of that, and you should get another broadcast packet confirming you're in safe mode. Then the box is on 192.168.1.1 and you should be able to telnet into it.
If not, then yes the next move would be to attach a serial port. You need an RS232 level shifter, either make one using a MAX232 chip or hack a mobile phone data cable. There's info on the Wiki about this. It's not hard, but you should not have been running Kamikaze in the first place without one (this is said over and over again)
If you were happy with WhiteRussian RC5, then perhaps you'd prefer to run RC6 instead.