no 3x3 MIMO just i replace sr71-15 with xr5.Interesting radio card MMCX for 3x3 MIMO Operation , what antenna are you using?
Nstream dual is old u can always use N basically its better u use 1 frequency instead of two per link
but as u said if u already have XR5 and 433 - take a look at this post I've made it in 2009 - bonding
http://forum.mikrotik.com/viewtopic.php?f=7&t=35571
i have 2 RB433AH and 4 minipci XR5 and i want use nstream Dual.Can you sketch out a simple diagram of what you trying to achieve?
i want run NStream Dual.2 radio cards into 1 Routerboard is a very bad idea, as internal interference will effect performance