Hi,
To avoid speculations I would like to make the following statements:
1. If you use a pair of horns with the official RF Elements "Twin Horn Bracket" you will not see any MU-MIMO. Although besides MU-MIMO system will work perfectly fine.
2. If you use a pair of horns looking in the different directions you will not see MU-MIMO unless you do the following:
a. Connect one horn to chain 0 and 1, connect second horn to 2 and 3.
b. Update software to 4.5-RC and pick Omni antenna option under the RF settings.
2. If you use a pair of horns looking in the different directions legacy non-11ac subscribers most probably will work with single stream rates.
3. Spectrum analyzer will work only for the chains 2 and 3.
Thanks,
Dmitry