The H6 upgrade will work on your 2001 RS, as long as you have 16 inch or larger rims. I'm not sure of the offset, but I think all Subaru 16" rims will clear.
You may also want a buddy to help bleed the lines after, and it's a good time to upgrade to braided stainless lines if you're into that sort of thing.
Me personally, I like the balance of all four corners being converted to H6. Lots of people only use the H6 rear brakes with certain WRX front brakes for a certain balance. Might warrant some further research, but my 95 Coupe stops excellently, and feels great while doing so.