Yep, maximum 32 tracks on a Blu-ray disc. And yeah 720p24 is weird. It’d BD-compliant, but it’s not an HDMI-supported resolution, so all players do some sort of conversion before sending to a display – ideally upscaled to 1080p24, but many players are less than ideal, so you never quite know for sure.
AFAIK, there is no 720p24 standard in the HDTV specifications, but this limit is not related to HDMI. Could you please tell me more about the HDMI-supported resolutions?