Fiveoh: I don't know the history, but I can tell you the LS2 and the LS6 SOUND similar in specs but are actually quite different.
The LS6 is the engine that first appeared in the 01 Z06 at 385 hp, and was improved for 2002 to 405 hp. This is NOT the engine in the current Corvettes, 05 SSRs, or 05 GTO.
The engine in the current Corvettes, 05 SSR, and 05 GTO is the LS2, and currently it produces 400 hp (390 in the SSR). This engine is radically different in its electronics than the LS6. It uses CAN technology (simplified: multiplexed signals in the vehicle wiring, so multiple signals over fewer wires).
It is this difference in electronics which makes Ls Edit, Hp Tuner, LFILive and ALL the current microtuners that work on earlier engines NOT work on Ls2 engines.