Hi! The 64 bit audio engine refers to the internal signal processing. You still record your audio files in 24 bit or 32 bit whatever you set your project settings to. The bit depth of the files you are recording has literally nothing to do with the 64 bit audio engine. The only advantage you get is if you are using lots of processing on lots of audio tracks. Virtual instruments do not benefit from the 64 bit audio engine and are still using the 32 bit engine. Also only VST 3 plugins benefit from the advantages and the software companies need to provide like “real” 64 bit versions of their plugins. For example Waves plugins do use a 64 bit audio engine but still put 32 bit out. A lot of the software companies need to provide versions of their plugins that fully support the 64 bit audio engine. You can actually take a look which of your plugins actually support the 64 bit audio engine when you open the “VST Plugin Manager” and come to the effects tab you can let Cubase scan which plugins are actually fully compatible with the 64 bit engine.
I did the test myself and at the current moment it looks like only Steinberg’s built in VST 3 plugins and my Plugin Alliance plugins support the 64 bit audio engine at the current moment (maybe I need some updates). After running this test and seeing that almost none of my plugins I use all the time are actually fully 64 bit engine compatible (at this very moment) and also instruments are not included I am a little disappointed. There are also quite a lot of companies that haven’t even realized that VST 3 is the current plugin format even after 10 years of VST3 so these VST 2 plugins they provide will never benefit from the 64 bit engine at all.
So if you actually own a bunch of plugins that already support the 64 bit audio engine and you choose to do a mix in Pro Tools and Cubase you probably would get better results in Cubase. If you are just recording audio files in Cubase and export them to another DAW there is literally no advantage at all.