Ok ever heard of Fletcher Munson Curves ? They basically show that your tone changes with volume. This means that you have to adjust your tone as you turn up.

If you can try turning on the vacuum cleaner, turn your amp up to stage volume and set your tone.

If not then during your sound check get a very long guitar cable, get as near to the back of the hall as you can and have a good listen to your self with the rest of the band. What do you sound like ? Try turning your mids or bass down a bit if you want more definition. Also laying off on the distortion can help !

best of luck dude