My experience is that Johannus amps in their lower and mid class organs leave much to be desired. For example the frequency response is not linear but more or less skewed to the Johannus system of tone generation. There is a marked difference when playing HW thru a Johannus amp even with relatively good to excellent quality passive speakers as opposed to the same HW setup using Crown amps. It's all in the ear(s) of the beholder.
I can't speak to the high end Johannus sound systems.
In an installation some time ago, due to budgetary issues, the client initially used the built in Johannus amps and were disappointed in the results of (in their words) - The highly acclaimed Hauptwerk software.. My comment -
Don't blame Hauptwerk.. Later after just "upgrading" to a Crown CT4150, they (all) were amazed at the difference. For one thing in clarity of the speech and in the very natural, detailed sound.
There are no built in cooling fans., not needed., amp runs exceptionally cool even at full rated power - 125 watts.
These amps have a built in feature of being able to (remote control) mute and unmute the speaker outputs allowing for being able to silence the speakers while listening via a headset.
A review of the 8 channel version CT8150
https://www.youtube.com/watch?v=yzK_p70BC8wRgds,
Ed