1st digital mixer -More busses than aux's - confused (or possibly stupid!)

Beexter

Hi all, 
I've recently bought a Behringer X Air XR16 as a compact solution to my analogue desk setup.
It's my first foray into digital mixers having only used small analogue mixers and I'm a bit confused - the XR16 has 6 aux busses (plus another 4 FX busses) but only 4 aux outs.

On my analogue desk, there were only 2 busses and 2 aux outs - I used one to feed an external reverb unit and the other for the monitor mix. 
I appreciate I could provide 4 separate monitor mixes from the 4 aux outs on the XR16 but what is the purpose of having 6 busses but only 4 aux outs?

Danny1969

Buses are for grouping things which might not need a physical socket to exit the mixer ... drum bus to main L & R for example. 
Aux sends are used for internal effects and external sends to monitors .... therefore need at least some physical sockets to get the audio signal out the desk in analog form. 

So bus just means a group, could be internal in pure digital form with no physical socket and no DA convertor 

Aux send can also be pure digital for internal processing but will generally also include a DA convertor and socket so you can get the signal out of the desk and on to a monitor - IEM - another FX unit etc