Paolo, it seems to me that there is rebranding going on. “Radeon Pro Software Enterprise Edition 18.Q1.1” is obviously the more recent iteration. (The other is referencing December 2017). As I mentioned, the most recent update is 20 March this year. It’s obviously disappointing that neither give you what you want - a stable, usable display output and provision of opencl using your AMD GPU(s).
You may find that using Andreas’ method works for you; it’s a case of your mileage may vary because of the huge number of variables: which exact hardware, which Linux distro, and sometimes the way you hold your mouth
Good luck, and please do share any success stories.