I was planning on using earplugs with the phones. With musician's earplugs, the music isn't distorted. With closed headphones, the treble will be diminished and the sound will be bass-heavy, making the plugs redundant. In other terms, I'm looking to turn the volume down without distorting the sound that comes in.
I can go with a closed headphone if it will isolate equally across the spectrum, or if isolation is minimal. I am looking at audio technica M30. Are those on-ear or over-ear phones? I tried M40 and they were good, although a bit heavy. I didn't like the AKG 240 and 271; they were too silent with too little bass. The 240 did not leak much, which was a pleasant surprise! The Sennheiser 280 was quite the opposite: a lot louder with plenty of bass and a very coloured image.
Another thing to keep in mind is that the phones must be loud to cut through the drums, so maybe I'm better off with a cheap headphone with low impedance of 32ohm than with an expensive headset. I know the M50 has low impedance and is high-quality, but it's also quite heavy. If I have to wear them for hours, comfort is of course important.
If you have other suggestions, I'd be happy to hear them. However, I think open phones are the way to go because I do not want to block exterior sounds out. They just have to be loud enough and have good bass-response.