Max is 24/48. That means the audio can have a flat response beyond 20 KHz. A large part of the populace probably can not hear even 15 KHz so it makes little sense to have a response beyond that. If need be I can generate tones of 15, 18 and 20 KHz so you can test for yourself. Need to be careful, I know several that burned out tweeters trying to hear those tones.
Dolby TrueHD (including Atmos) data stream can go as high as 18 Mbps (18,000 Kbps).