The network adapters are not the only modules that will not work. Anything that requires a compiled module to work (ie. hardware...network adapters for example, software....masq modules for pptp, irc, h323, etc....) will not work unless you have a 2.4 version in place. You have a better chance of using version 5.6, then you do trying to replace every module.
Sorry, but I have had to change too.
HTH