I LOVE the HD650. I love everything about them... The highs of the HD650 are perfect for me! The mids are ASTONISHING. The lows are sooo deep like a closed can. I just put these on and I forget for a long time that I even have them on. The HD650 are definitely more comfortable than the DT990 600 ohms. The top padded part just felt too heavy on the DT990 after a while. Not with the HD650!!! They are sooo light. I also love how the wires run down from both drivers as opposed to just one in most other cans. The weight of the HD650 wire is evenly dispersed on both sides. ALLLLL these little things sum up to produce a luxurious set of headphones that are just mind blowing!
Absolutely... one of the reviews of the HE-500's on another forum report that with the right setup, the HD650s (assume new version) sound better than the HE-500's - but, that sound quality from the HD650's comes at the price of pretty pricey setup.