Upload & Sell: Off
I have the Sirui T2204X, and bought the Sirui K20X ballhead as a combo. This is the largest Sirui head that will fit within the legs when folded (i.e. so that the legs remain parallel).
The K20X is nicely made, smooth and stable. It solidly supports my 70-200 2.8 IS II (Canon). It's not as good as my Markins Q10, but it only cost a quarter of the Markins!
I don't know about your seller, but I got a reasonable discount by buying both legs and head together.