The back half of the xi is exactly the same as the regular "i". Anything will fit. Check the sticky up top for more info.
I have not tried the UUC sways, personally. I have read that there are some fitment quality issues, but who knows? I called to get some more specifics about their bars (arm lengths) and I got the sell that "you can't compare one company's product to another". Yeah, right. Without that info, it is tough to get figures.
However, most knowledgable members say that as long as you have stock spring rates (stock springs or eibach springs), the UUC bars should work fine. Just don't go crazy adding them to other setups. Just because it handles flatter does not mean it handles better.