The 54xx does not have the requirement to "enable jumbos for your LAG group as well as your ports" since the setting for jumbo frames on the 54xx is global, not per interface.  
It seems to be pretty well documented on how to enable jumbo frames on individual or all ports, and it also seems to be mentioned quite a bit to make sure that you change your LAG to jumbo frames, but I cannot find the command line syntax on how to do that, and how to verify that it is set correctly afterward.  Any ideas?  I'm trying to do this on two powerconnect 5424's that have the first 4 ports on each switch, in a LAG, with STP turned on and all of the other typical settings.  
Changing an LAG to work with jumbo frames...