Lots of food for thought, thanks for the replies everyone, I appreciate it. I don't know if anyone has any specific experience with my amplifier:
Marantz Europe because I'm wondering how good the headphone out truly is. I have to be honest, I'm more a speaker kind of guy but during late night listening I still want to enjoy some quality tunes.
Right now, I'm leaning towards the HD-600, at the price they look really tempting and after reading alot, it seems to me that I would like them more than the HD-650.
The price on the denon was an estimate, it was the official list price and I hadn't found any webshop yet that sold them at a lower price. The Amazon links is very usefull, thanks but I don't think I'm willing to pay about 100 euros more for them.
Right now I really do feel that the HD-600 would best for me, about them being easier to drive would be easier to drive by my current amplifier. I'm sure they will respond to a future headphone amp upgrade, am I right by assuming this? If I want to see a clear improvement over my current amplifier, how much should I be spending? I know that quality equipment costs some money so I'm willing to pony up the dough. It's an expensive hobby, or atleast it can be, but it's oh so rewarding.