I am planning on buying a new shifter for my G27, I don't want to change wheel. I dislike the G27 shifter due to two things: Lack of modability, eg: How heavy the shift is, 2 Gear sequential. And my second problem, 2-3, 4-5 gears. It is easier with the TH's. Which is better, and which works with the G27? I can't tell if they are the same, there isn't much on the TH8A, so I am wondering. They both look the same which is another problem. Here is a review of the TH8A: I post that, because I also want to find out the intro song of TheSLAPTrain. So yea... Thanks.
From what I've read, the RS is a standalone shifter and the A is an add on shifter for TM wheels, but can also be standalone. The only real difference is in the connections.
I don't know if its compatible but the g25 shifter does sequential. You may wan to look into it a bit since you may be able to get one pre owned for not too much.