I had the same issue after the update. I was about to revert back to 4.5 Artist but, I tried one more thing. I went to Studio One Installation in the menu bar and re-installed Ampire XT Classics. That brought back all of the amps I had previously and took away the On/Off icon. One more thing, the levels of the amps are different so, I had to remix every instrument that I had using Ampire. I hope this helps.