5.0 Recordings. Question on Bass Management

Didn’t know if this was best in the H.T. Section or Digital.  Here goes.  One of my favorite Classical Labels is the Swedish label BIS.  They still support SACD and surround sound, but in a  5.0 configuration only.  My question is what happens in a system where the sub is being called upon to supply the low end.  One of my HT systems has monitors as fronts, and the sub handles everything below 80.  The AVR is an Anthem 520 and on most 5.1 recordings the low end is pretty reasonably reproduced.  The monitors are capable of going into the 50s but work best with the sub handling the low end.
  When listening to a few BIS SACDs recently I was negatively impressed by the low end, which sounds pretty malnourished in this system but just fine in my 2 channel system.
  My question is: Does the Anthem AVR recognize that there is no sub, and then just let the monitors wring as much low end as they can?  Or is it still cutting the low end at 80?