yup, you are absolutly correct. I have a 2007 G35 Coupe 6MT, with Rear Active Steering. I have done some research as well, and even contacted HKS. We can not use any exhaust system that deviates from the stock exhaust pass.
I have just ordered tanabe madalion touring with y-pipe today. I took a gamble on it, because no one knows if it is compatible, due to the fact that RAS is so new on our vehicle. It comes in next tuesday, I'll keep you posted!
I have a 2007 G35 Coupe with RAS and the HKS exhaust. Some rubbing on the RAS but I put a piece of rubber around the pipe with two worm-drive clamps and that solves the problem.Did it end up working out? can you post some sound clips