My at-the-office setup consists of Sennheiser HD650's and a LittleDot MKII Tube amp. They are fed a diet of lossless & 256kbs AAC and the occasional 192kb Pandora stream. In a word, heavenly.
I've had the setup for a couple of years, and I remain exceptionally satisfied with it. When I bought the HD650's, I also bought a pair of AKG701's. My budget would only allow one pair, so I spent a good couple of weeks agonizing over which to keep. I burned them in as best I could. The 701's are *great* headphones. They are exceptionally accurate in their sound. Crisp highs that will overblow on a brightly-mastered album, wonderfully accurate midrange, and tight bass. Very much like my Axiom speakers. But they *will not* sound very good if you try to drive them with the an iPod or some other MP3 player. They require a good, dedicated amplifier. Seriously. Otherwise, they sound feeble & scratchy. The HD's also need good amplification, but they are more forgiving from being powered by an iPod. The HD's have a slightly warmer midrange to my ears that really livens-up the kind of music I enjoy listening to. IMHO, it's a more 'intimate' sounding headphone than the 701's, and that was (and still is) appealing to me.
It was a very tough decision, but I chose the HD650's. I actually preferred the cosmetics of the 701's (they look 'special'), but the SQ won. Comfort was a wash - they were both great for multi-hour sessions. I wear glasses, so that is an issue. To me, the HD's just sounded better with the jazz & classical music that I enjoy listening to. I couldn't (and still can't) get over how rich and textured these cans sound. Sublime. I love my Axiom setup at home, and this HD650+LD pair gives me what I have at home but in a headphone experience. The soundstaging and dynamics are unlike anything I've ever heard in headphones. It's sinfully good, if I do say so myself.
It took a lot of courage for me to spend $500+ on a set of headphones and the amp (that's a lot of money!), but I can honestly say it's one of the best audio purchased I've ever made. Easily on par with my satisfaction of my Axiom speakers.
All that said, I also have a pair of Grado SR60's. They are great, and well worth their meager price. If the HD's ever break (
) , I would definitely consider some of the upper-tier Grados as replacements, as I would imagine they are fantastic given how good the SR60's are.