Its not too much of a blind buy if you understand measurements because they essentially tell you if they are complete shit or not. They measure very well in terms of frequency response, have pretty good distortion, don't have most of that funny CSD business that most semi-closed and closed back headphones have that makes them sound cavernous, and they lack any of the treble emphasis of most bass heavy headphones like the TH-600 or TH-900. Its a bass heavy headphone that doesn't sound like a one trick pony, can take EQing pretty well if that's your thing, and probably doesn't sound like a typical closed back headphone.
Add in wood cups, an actually a pretty good price for what are essentially flagship headphones, and Jude over at Head-Fi hyping them up and they're obviously going to sell well.
The HD598 into your receiver is not a good idea. High output impedance from the receiver's headphone jack + Sennheiser's house impedance curve + the HD598's high bass distortion = bass mud galore. In such a case, I'd take output from a smartphone, computer, or laptop over the headphone out from a receiver.
