Is there any chance that shots were fired outside, hence no additional bullet holes in the wall, casings on the ground, etc. I know that's a real long shot here, but just thinking out of the box about the additional gunshots heard by Stipp.
When it all boils down, we really have about a minute of time that we're stumbling over.
Stipp is woken up by what sounds like 3 shots. Maybe it wasn't exactly 3. (oh crap, do I sound like Roux?) There could have been screaming beforehand but it didn't wake them up. I can't explain that, but it's possible. He says he was up and on the balcony within moments, which translate to seconds for him. He heard the screams, saw the bathroom light on, went back inside and picked up his phone to call security. While he is dialing, the second round of shots go off. This sounds to me like a very brief window of time, could even be less than a minute.
Burger & Johnson hear screams then a gunshot. A pause... then 3 more gunshots. Maybe the pause was longer than they realize. They heard screams throughout the shots, so to hear screaming there was some time occurring between shots.
It could be that these 4 shots happened within a 30-60 second window of time and we're all just hung up on how long the pause was after the first one. When an unexpected traumatic event is happening to you, you really have no sense of complete accurate time. All you can do is estimate because your senses are so rattled.
Am I making sense or do I need to go to bed?