I frequently hook up my MacBook Pro to my iMac in Target Display Mode, and use my iMac's speakers.
The big drawback with this setup is that the volume control is grayed out in the menu bar of the MacBook Pro, and its volume media keys do not function.
But, according to this Apple support article, it shouldn't be this way:
You can control the brightness of your iMac display while it's in Target Display Mode from a connected Mac. Use the Displays pane of System Preferences on the connected Mac, or use the brightness keys on the keyboard of the connected Mac.
To hear audio from a connected Mac using the built-in speakers of your iMac, select the iMac from the Sound pane of System Preferences. You can also use the sound and media keys on the keyboard of the connected Mac to adjust volume and control playback of iTunes and other media.
For what it's worth, I cannot control neither the display nor the volume from my MBP.
Instead, I usually have to change volume by using the volume keys on my iMac keyboard. I guess other workarounds are possible too, but they all involve the inpracticality of not being able to use the native volume keys where I'm typing.
Can this issue be resolved somehow?
N.B.: I'm using Thunderbolt 1.
N.B. 2: I've tested this a bit further. After a reboot and reconnection, I could actually use the volume controls; but not the display controls. Either way, since this problem is frequently occurring – what can I do about it?