Play aggressively with the Emperor, otherwise he'll get smacked before he gets in range.
At least the Emperor can outrun and outrange the OEM Rhino. I STILL have a devil of a time getting a decent shot with mine, I really don't mind the short range on the guns, it is my inept handling that needs to be fixed. Now, the Thunderhawk, THAT is a SuperHeavy that sees regular use in my forces now, longest ranged weapons of any SuperHeavy and maneuverable enough to stay away from superiority Cavs.
What has been the biggest problem with your Emperor Sarge? Enemy air, or Cavs with longer range? My Rhinos keep getting smacked by Air strikes primarily, no one else plays Terran here and most people don't use artillery that much, including me.