I understand that AirPlay is an important feature of the Apple TV, and I would be concerned too if the audio was not working using AirPlay.
Because both your MacBook pro and your iMac are very new (congratulations!), I recommend first checking to see if your Apple TV has the latest updates:
To update your Apple TV to the current software version:
- Select Settings > General > Update Software. Apple TV checks for an available update; if one is available, a download message should appear.
- Click Download and Install to start the download process.
Do not disconnect your Apple TV during the update process. The Apple TV status light may flash slowly during the update and restart process. This is expected behavior.
If your Apple TV is up to date or the audio is still not working, I recommend following the steps in this article:
Thank you for using Apple Support Communities.
Thanks for your message i've tried all the things you've suggested and the problem is persisting. My settings say that the sound from both macs is supposed to be going through Airplay onto the Apple TV but there just isn't anything coming through. Is it possible this is an oversight in Mavericks?
Thank you for trying those steps and providing the additional information. Due to the nature of your issue or question you may find more information by using another one of Apple's support resources - https://getsupport.apple.com/GetproductgroupList.action
All the best,