I just re-read your question again and I'm not sure that CV8, decoder resetting is the solution. A few questions might bring a different answer.
1. I note that you said that the sound was lost on all the decoders. Did that happen all at the same time, ie. so they all worked fine and then none would work?
2. Do the motor commands still work ok?
3. Do any of the other function sounds work at all?
4. Was there some event that occurred just before they all stopped working?
If the answer to Q1 is yes, it may be the PowerCab which could need a reset. Their instructions for resetting the PowerCab are at
https://ncedcc.zendesk.com/hc/en-us/articles/201251979-Reset-Powercab-to-factory-defaults
Hope this helps.
Julian