sunnyside

I have always had good luck with Goodridge Stainless brake lines. The pedal feel will be solid and will improve the factory brakes. Tirerack may have what you need. Replace the factory pads while you are at it and you may be very surprised.

Clutchless

I think a big issue with the RX is the designed in mushy brake pedal feel. It is hard to eliminate, even with better pads, and bleeding and I doubt steel brake lines will make much difference. I do not know how to change that pedal feel, maybe free play adjustment? But wish it were possible.
I recently drove a friend's 2003 Honda Accord with 108,000 miles and was shocked at how grabby the brakes were compared to the RX.

coolsaber

Brake feel unless its FBW, is directly a product of brake lines and of course the master. If you can improve one of both you can achieve the grabby feel you desire. Only problem is that changing the master is probably out of the question for most folks, stainless steel lines on the other are doable. However its going to be expensive if an aftermarket specialist has not decided to make a kit, and you do loose some safety margins built in if you buy something you dont know what quality it is.

For instance if your purchasing stainless lines, make sure they are from a reputable mfg who pressure tests the lines, and of course cover them in some kind of plastic sheath to prevent road debris from wreaking havoc on the braids.

sunnyside

I checked the Goodridge site and found nothing for the RX. I bet that a set could be made or perhaps the one for the Toyota Highlander would fit.