I have the Beyer DT 250's, and I love them. I tried out a whole bunch of Senn's and the Beyers and some AKG's and liked the beyers the best. They go good and loud, the sound quality is good, minimal spill and they are the most comfortable phones I've ever worn (my head is not small, and I have trouble with crappy uncomfortable phones).
Cans? Cans you say? The Beyer cans are exceptional. Yea, verily, so are many other cans by Yamaha; but, how many models does Yamaha put out?
Beyer has a couple of models; I have two sets in my studio and although the headband is a bit tight, the sound quality is great.
I also use a pair of wireless cans when I am doing copy work in the studio as they give me walk around freedom and I don't need to "hear" as well as in other types of work.
Beyer cans are in the mid range price spectrum but, more expensive than many other types of cans.
Well, can I say you will get cans that can serve you well.
I agree that you should also consider the Audio Technica ATHM40fs. I use them to great use. They're not as comfortable as the Beyers, but are IMO in a similar quality of accuracy (the Beyers are a bit more open and at a slightly higher level for a much higher price). But with that said, the Beyers that you speak of are great! The imaging and sound quality it very good and the headphones are the most comfortable that I've worn. I haven't ever tried the Sennheisers that you speak of so take my comments accordingly.
Thanks for the input guys. I went ahead and ordered the DT-831. I'll let you know what they're like when I get them. The only cans I can compare them with are AKG 240 that belongs to a friend.