On TSX CL9, the header is placed between the engine and the subframe, while on the DC5 RSX runs between the subframe and the mylowes firewall. The manifold has a built-in cooling port, while the RSXS manifold uses separate housing. To replace the manifold, Hasport has developed an adapter plate allowing any K-series intake manifold, separate mykohlscharge throttle body or turbocharger made for the RSX to be adapted to the TSX.
I highly recommend littebo's header, very reasonable price for the gains and overall quality which is excellent. Also he can set you up with a hfc or test pipe designed to bolt up to your current exhaust. You can find him on here.
I second Littlebo's headers based on the positive feedback others have given. I personally do have them as they weren't available when mine were made but that's what I would have gone with if they were.