As long as Audyssey is on, sampling rated will be 48 kHz. Even if Audyssey is off and you are using direct mode, you still won't get 192 kHz for Atmos movies. And if it did (but it really didn't..), if you heard improved sound, you were just thinking you heard it, that you really didn't, sorry.. but that's the truth.
How loud do you listen? What's the volume setting and what's the level trim settings for the main channels post Audyssey? Unless you listen to near reference level, that is too loud for most people, you should turn dynamic EQ on and dynamic volume off. Audyssey typically would level off /flatten the bass from 20 to 200 Hz and most people don't it flat from 20 to 200 hz. You can compensate for that by increasing the subwoofer level (via the speaker/level menu) by 2 to 5 dB, though a better way to do it is by using the editor app that allows you to customize your own "house curve" for the 20-200 Hz range.