Using a RaspPi 4 in the Pisound case, with 4 small heatsinks on the RaspPi with a PureData patch in use, I found the running core temperature to be between 60 and 66C. Which I think is OK vs the throttling temperature of 85C (I think).
Ideally I like to have have some margin, so I tried running it naked - about 45C.
The pisound case helpfully allows for panels to be removed. Taking the top off made no big difference. Nor the side by the GPIO pins. Understandable. With the side by the audio jacks, which has most free space for heat to escape, it ran about 55C.
I might run it like that, or maybe add some vent holes to that panel. It looks like there is more enough room to add a bigger heatsink, which might help a little too.