We used three pieces of 4'x4' sound board to create a surround for the drum kit. We used some short pieces of coat hanger wire to hole them together at the top corners. Getting the sound board to extend above the cymbals is very important. Depending on where the drum kit is set up placing another piece of sound board or even a piece of hanging carpet behind the kit may also help. Another idea I had but have not tried is to hang another piece of sound board above the drums and slightly angled away from the other band members.
IME, this really reduced the noise factor, the need to turn up the volume and allowed the drummer to hit pretty hard w/o everyone getting on his/her case. To hear the kick drum we placed a mic in it and added a bit of volume just enough to get it in the rehearsal mix. I think cutting a hole in the sound board in front of the kick drum would work as well.
Another thing we did is to staple carpet on the wall/ceiling studs to soak up a lot more of the "noise". This deadens the room substantially but also can "cleans" up the overall sound even more. Carpeting the floor also helps.
If you can get the all the amps off the ground about 3 feet or tilt them back and point them at your head would also helps reduce the need to turn up the amps.
Also, a friend of mine used to hang 1x15/horn p.a. cabs up about 7 feet and pointing down and at the band to hear the vocals better.
Picking up a db meter may help to convince everyone to turn down. Doubt it since they are telling you to get ear plugs.
