I love the Ampli-firebox, but when I tried to use it live at my church, it gave me fits. Connecting it to the PA using the built in XLR output made it have a high pitched constant sound, almost like the sound of water running. The sound was not quite hum, and not quite static. That sound overpowered the rest of the signal from the Firebox. Plugging it in through the 1/4 inch output and then to a stand alone DI, seemed to help knock out almost all of the sound, but it also made everything substantially quieter to the point of being unusable. I cranked every setting and the sound guy maxed out my channel as well, but it was still barely audible. I ended up pulling back out my old Line 6 Pod and using it, which incidentally worked perfectly using the exact same cables and channel on the PA. Later that day, I tested the same configurations with the Firebox at home using my FRFR, and everything was perfect. No weird sound or volume loss at all. So I am stumped. Here is everything I have tried, hopefully one of you awesome people can help me figure out what is going on, otherwise, I may have to return the Firebox, which would kinda stink since I really do like it a lot. 1. Tried to see if it was a power supply issue. I started out running it through my pedalboard power supply, as recommended in this thread: http://atomicamps.com/forum/index.p...-powered-through-pedalboard-power-supply.995/. I then immediately tried using only the original power supply that came with the Firebox. Same sound was present. 2. I thought it might be some weird bleed-through from the other pedals I was running in front of the Firebox, so I disconnected them and ran only through the Firebox. Same Sound. 3. I tried to see if the XLR cable going to the PA was bad. Three different XLR cables and two different channels on the PA, all with the same annoying sound. 4. Tried using two different 1/4 inch cables between the guitar and the firebox. Same Sound. 5. Swapped out the surge Protector being used. Same sound. 6. Tried my back up guitar. Same annoying sound. I ultimately tried every combination of Guitar, 1/4, XLR, etc. Everything worked perfectly in conjunction with the Line 6 POD, but got the annoying sound with the Firebox. However, the Firebox works perfectly through my home rig. It seems to only give me fits when used in conjunction with this PA system. I am playing at another venue this weekend, and I plan to test it out there as well, but I play in this particular church every Sunday, so I either need to find a way to make the Firebox work, or I will have to move to an alternative. Additionally, I was using factory default settings on the Firebox. I hadn't had time to tweak any of the settings, and frankly I liked the sounds as they were straight out of the box. I tried every preset, and all had the same sound. I also tried changing the CAB IR switch between the Cab XLR/Cab 1/4" as appropriate. Nothing I tried helped. And I know thats a lot of text to read, but I want to be thorough, and I really need help.