I've downloaded Jack and gave it a try.
First thing to fix in MorphOS installation is a path to IconX in install icon from SYS:c/IconX to MOSSYS:c/Iconx, that's why installation didn't work.
But there is something wrong with installer as it doesn't copy stuff and doesn't create a new drawer.
I've copied files from $jack_destination to a proper drawer and then copied MorphOS executable to that drawer as well. After that I got a popup asking for a language and then it fails as it was unable to open transparent windows. ATM im using a gfx card with no 3d support so I presume that's the reason. Will do some more testing tommorow with 3d supported card and let you know.
But at the start u need to change path to iconx and have a look at installer where is the mistake.
Regards