I have a suspision that once you are banned, M$ writes something or marks your EEPROM or something, and it prevents you from connecting to live (kinda like live preventing mod chips). The reason I think this is, when you connect to live, it takes a while to send data back and forth, but when you are banned it IMMEDIATELY gives you an error, like its not even trying to connect.
Heres what I would like someone to try, if possible.
1) Take an xbox that is on live and working fine. Doesnt matter if it was banned or not, but preferably one with a stock HD (not sure if this would matter)
2) Obtain a previously banned EEPROM (im sure there are plenty of these hehe)
3) Unlock the hard drive and flash the banned EEPROM onto your xbox
4) Manually change ALL of the values of the banned EEPROM to the values of the working non banned EEPROM
4b) You may want to do an evox backup and compare the eeprom values on ur computer using any eeprom viewing utility (cant remember the name of it)
5) Lock the hard drive and try signing in.
this should NOT violate the old 'marriage theory' because you are using the same EEprom values and the same hard drive, and in theory you should be able to sign in. If you cannot, it supports my theory of eeprom marking.