manual/include/comparing-aux-sends-and-subgroups.html

<p>
  Auxes and Subgroups share a common concept&mdash;they both provide a way 
  for one or more tracks (or busses) to send their signal to a single bus so 
  that common signal processing can be applied to the mix of their signals. 
</p>
<p>
  <dfn>Aux sends</dfn> leave the existing signal routing to the main mix in place, 
  and are typically used to create a separate mix to send to (for example) 
  monitors or headphones (for performer monitor mixes): 
</p>
<img width="300px" src="/images/aux_routing.png" alt="aux signal routing" />
<p>
  <dfn>Subgroups</dfn> usually remove the original signal routing to the main mix and
  replace it with a new one that delivers the output of the subgroup bus to 
  the main mix instead.
</p>
<img width="300px" src="/images/subgroup_routes.png" alt="sub group signal routing" />