To be honest if you're not doing track days or really caning the arse off your car the stock NA front 2 piston slider calipers ain't as bad as people make out and are more than up to the job,for me they are anyway. Considering these brakes are also fitted as standard on some of the other heavier Lexus cars,more pistons aren't always better and when I think of my grail car the Honda NSX the front brakes are also sliding 2 piston calipers not multi piston jobbies.
Chris Wilson wrote a very interesting article on making the ordinary stock NA front brakes perform nearly as well as the UK front brakes even on track days.