i don't know if this is the right place to ask but i'm planning on buying an hks legamax premium + hks center pipe + hks down pipe. my question is, is this a good combination?

 

exhaust tubing is...exhaust tubing...lol. Aside from different size diameters and thickness steels and materials (Ti, mild steel, stainless etc) there is not much to it. Muffler design affects a little bit but not much and catalytic converter cells per cm can have a good effect but as long as you get a decent made exhaust it is not going to matter much...If anything I would add a test pipe or HFC to your setup and you should be good to go. Definately need a tune though!!!!!!