use multiple controller with rekordbox

I have a ddj-flx10, ddj-1000, ddj-flx6 & a ddj-xp1, now if i power up the ddj-1000 till its booted then connect the DDJ-flx6 then open rekordbox it will detect both and allow me to use both controllers to control all 4 decks at once & will allow me to enable the DDJ-XP1 once rekordbox is loaded, i tried to replicate this trick with the DDj-flx10 & the ddj-1000 or the ddj-flx10 & the ddj-flx6 & it wont work together, yet if i connect the ddj-flx10 & ddj-flx6 together they will work in serato dj, its not a hardware issue or it would not work in serato, why have pioneer(alphatheta), made it so i cant use 2 controllers at once, if you have 4 decks you should be able use them with multiple controllers, traktor pro 3 allows this, serato allows this, virtuall dj allows 99 decks & the gear to run them i spent around £3000 on gear, it should not limit me to one controller