Yup... the HD650 adds a warm, wooly character, and it takes the edges off a lot of recordings. Its a good complimentary can to my K701, RS1, A250. I have to watch out with volume settings, being that these are a more laid back sound and one can unknowingly turn up the volume to compensate. The image and soundstage is not as vast and layered as the K701 though. So thats kind of a bummer, but I knew this already. I can't tell if its the 701 adding something to the image, or its the K701 detail resolution allowing the ambience and space in the recording to show (I suspect its a little both). My 650 pads are worn and soggy though, so it might be time for a replacement. That could be compressing the image inwards a bit.
You're allowed to turn the HD650 up here and there...that's the whole point of the frequency balance. Mids and bass is not gonna wreak your hearing when at reference db than brighter cans, which will slice your ears off. The hearing becomes is more resistant to damage as the frequency falls. Real music is played at a reference db. The HD650 is very neutral at reference db. Of course don't do it for too long and not too excessively - plus you'll need a majorly powerful amp to do this without compression and distortion.
You'll know when it is time to turn the volume down - your comfort levels are the warning systems.