the only incompatibility (i think) between the 2nd gen ipt and older speaker systems w/docks is the lack of firewire charing support. what i mean is, you can still play music fine through the dock connector, its just the speakers can no longer charge your ipod.
you might want to double check with appl, or try ilounge.com. they have reviewed almost every ipod speaker system in existence and are probably a really great resource.