I'm unsure about the RSX however I know that coilovers from a DC5 will fit an EP3 and visa versa if some minor modification is done. Can't remember what exactly.
Rsx and dc5 are interchangeable,
DC5 and EP3 are also BUT to use ep3 kit on a dc5 you will need ep3 track rod ends and 4 x1mm (ish) 2 per damper, spacers for the lower rear mounts as an ep3 has a narrower bracket