Hmm.. It wasn't mentioned any where on PC home website or on the box but according to Ducky Channel website:
"PS/2 interface: can press all keys at once, USB interface: can press up to 6 buttons at once"
I know that website is for the normal 1087. I'm not sure if the NKRO support extend to their XM series as well.
I just got mine delivered this morning, it took about one day.
and, Thanks for the review.