Generally the guy running sound has a gain control where he can adjust the level of the signal you are getting. You obviously don't want to pester the guy a lot and piss him off, but I think it's fair to ask him ONE TIME to raise or lower the levels... I set my gains to mid-range and if I have something between peaking and -40, I'll say "good enough, thank you!" and then I'll adjust from there to bring it in closer. Don't even think about bothering him just as the band gets going, but a couple of minutes into the first song is probably OK. So the first couple of minutes of the opening act might be a little rocky...
Perhaps some of the guys who run FOH can give us their perspective on my statement.
If you really want some attenuators, I think the ones that have switches for 10-20-30 are probably not much more than the ones with fixed 25. I kind of doubt you need 40db.