My understanding is that that the LS2 heads are materially identical to LS6 heads. Whether or not CTS-V/Ls6 headers will fit an '06 CTS-V is another question. One way to determine this is to compare stock exhaust part numbers.
According to TPIS, the intake manifold design of the LS2 is substantially inferior to the LS6. TPIS is currently working on a way to mate the 90mm LS2 throttle body onto the LS6 intake.
According to TPIS, the intake manifold design of the LS2 is substantially inferior to the LS6. TPIS is currently working on a way to mate the 90mm LS2 throttle body onto the LS6 intake.