to chime in. i installed the RB bar on my LX and you do need the mazdaspeed endlinks for the rear. The sub frame is optional because everything hooks up as it should with a regular subframe and not the MSP one. i believe on the MSP subframe the tabs that the stock bushings bolt into are beefier and that is the only real main difference.
being i have the clunk fix kit i dont have a need to worry about that. since installing everything, the car has handled beautifully. not one complaint other than the bushings wearing out and squeeking and such. make sure you grease them or do what i did. go to energy suspension and get the 19mm
bushings so its a super snug fit and when they wear in they will still fit nice.
the tabs on the stock struts tend to be a little weak, so with a bigger swaybar and more stiffness. they are prone to snapping off. I recommend the tokico blue struts or the mazdaspeed protege struts which are also tokico blues, just tweaked a little bit. they offer a sturdier tab and stronger welds in general all over.
when the bushings that come with the clunk kit wear in/out, they become loose and make noise do to the bar wobbling around inside them. aka "the clunk". also bad endlinks can cause a clunk too. not fun.
hope this helps.