I ordered my dna version from fasttech (i am pretty sure) and would suggest you do the same. A brand new dna version ($95-120) is a good deal. They sell 2 versions of the dna one with usb another without. Get the usb version. Also the dna version is worth the extra money.
Make sure you buy a rba because the included kanger rba is not very good. Avoid the boxxer rdta. The included aspire bridge works good but the kanger occ bridge gave resistance issues. Being a cheap knockoff bridges included there is really no telling which ones will work for you.
Most authentic billet box accessories work with the sxk. The authentic rbas and bridges work better than the clones. Although I would suggest trying the clones first to find what you like. Then buy the authentic (new or used) rda/bridges.
From what I understand the only part that you cannot interchange is the negative screw connection on top. The threads are not the same.