There’s an important difference between v1.0 and v1.1 Pisounds that can affect your experience with Raspberry Pi 4 (and most likely Pi 5 as well) - due to a power supply design change between Pi 3 and Pi 4, sometimes restarting the OS could hang. We had to make a change on Pisound side to work around the issue, but there’s a software fix available, all the details are in this thread:
And the general specifications section of the documentation:
As for temperature - Pi 4 can be used fairly successfully without any heatsink or fan, Pi 5 is better used with their Active Cooler fan & heatsink, otherwise, Pi 5 will not run at its full speed.