What I did was, that I created a SoundMix that affects Sounds in the SFX sound class. (Of course you need to properly setup your sound cues, but you’ll want to do that anyways)
That sound mix then adjusts the pitch. Probably not the perfect solution and I only did a quick and dirty implementation.
You only have to make sure that sounds are assigned to the right sound class.
When calling the slomo function I also apply the sound mix modifier and remove it when the slomo stops.