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?

So this depends on how you set your main speakers.  If you set them to large they will not pass bass to the sub.

If you set them to small then they'll use the crossover setting.
If the SACD remix is only intended for 5.0 (L, C, R, LS & RS) then there is no information being sent to .1 (sub). In case of BIS SACD playback, I would ensure your speakers are configured as full range. 

You can’t expect your AVR to magically reproduce the low end bass that isn’t there to begin with. Here is what I’ve found on BIS website,

“Our surround sound recordings aim to reproduce the natural sound in a concert venue as faithfully as possible, using cutting-edge technology. With some very few exceptions, they conform to the so-called 5.0 configuration, in which all five channels are recorded using the full frequency range, with no separate bass channel added.”