With Audyssey, you can turn it off/on with the push of a button, which I do often. This way you can hear the difference with no room correction, compared to just correct delay, and matching dB levels. Audyssey always sounds better in my opinion.
mpyw, you never want to lower the crossover to below the setting found by the Audyssey/Receiver setup. When doing this, you are creating a hole or gap that is not getting corrected. Either adjust and rerun the setting to see if you get different results, or don't use Audyssey. It is ok to bump up the crossover from the findings, however.
