I'm afraid there is no way for the particles, apart from doing you own particle generation with sprites through events.
Controlling the audio channels is a lot more easy. Just uncheck "Timescale audio", then select all the channels that you want to be affected by timescale, and set them to a frequency fitting timescale.
+ System: For "" from 1 to 5
-> XAudio2: Set channel LoopIndex frequency ratio to TimeScale