Yes I would let the mic driven set up do it's thing first, then if it does not set the crossover to 80Hz I would change it.
Anything lower usually results in the centre channel being muddy as it is dealing with too much low frequency, anything higher and I find the mid range is usually missing.
If you set it to 80Hz then your sub will be doing all the work, which it can handle easily, this will leave the AVR to concentrate it's power on what it does best.