Considering the automatic RX-8 only has 197 flywheel horsepower and weighs over 3,000 pounds, it's not suprising.
RX-8's have similar power output and the S2k weighs around 200 pounds less, I'd say that yes, under perfect racing conditions an S2k would most likely outrun the RX-8.
The RX-8 is also a four door sedan. If you want to race something more appropriate to the S2k's class, stick to FD RX-7's. In good running stock condition, they will outrun an S2k no sweat.