Sounds don't play in Dir 12 projector

It sounds (no pun intended) like you have a missing xtra. Scan through the list at Modify > Movie > Xtras ... looking for likely candidates to add. If you find any, try adding them, save and re-publish

A quick follow up: when you say

Each sound is placed in sound channel 2 with a 'wait until end of sound' in the timeline channel.

are you referring to a behavior/script you have added to the script channel, or a setting in the Tempo channel. Those settings in the Tempo channel should always be ignored and a script used in their place.

why are these 'wait' tempo settings offered as an option if they should be ignored?

I think it's a legacy from years ago (Director 4) when scripting capabilities weren't powerful enough to bypass some of the options the tempo channel offers. For example, here is a behavior that will wait for a sound in a channel, but isn't limited to channnel 1 or 2:

-- Frame: wait for sound in channel
-- can only be attached to script channel
property myMonitorChannel

on isOKToAttach(me, sType, sNum)
  return (sType = #script)
end

on getPropertyDescriptionList
  pdl = [:]
  props = [:]
  props[#comment] = "Sound channel to wait for:"
  props[#format]  = #integer
  props[#default] = 1
  props[#range]   = [#min: 1, #max: 8]
  pdl[#myMonitorChannel] = props
  return pdl
end

on exitFrame me
  if sound(myMonitorChannel).isBusy() then _movie.go(_movie.frame)
end