The price difference between them is about a 100 dollars, though. I posted a question at the Amazon website inquiring as to why such a price difference exists, and someone answered it's because the more expensive "model" is "high-rez". When I read this kind of nonsense, my head hurts.

Double post. Sorry.

  . I see your musical preferences have changed quite a bit since the 70's. Maybe that helps keep the tinnitus away, but I find the wide dynamics of classical music can catch me off guard. Sometimes I turn up the volume to better listen to a quieter moment, then suddenly the orchestra goes wild...

I have it in both ears. Louder in my right ear. Not a ringing or whistling sound, but a hissing sound. Sometimes it's louder, sometimes softer, but it never goes away. It's always worse if and when I pay attention to it. My ears are almost 50 years old and definitely not high end. It's just...

Why not a crossfeed implementation?

I'll compare my ole HD580s against newer models any day.  

You will essentially be using an HD600, then. Except no faux-marble finish.

I've bought my HD580's in 2003 and have been using them ever since. Recently, I've replaced the drivers with new ones I bought from Custom Cable in the UK. I also did replace the pads once, three years ago. These cans sound so sublime, I might as well enjoy them for another 10 years. To this day...

    Well, I use the Downtowns at work and they sound great for the money. Perhaps the Fidelios' price/performance ratio is not as good as the Citiscapes'.

After a decade of loyal service, I've replaced my HD580's drivers. Got the capsules from Custom Cable in the UK. Now they are ready for an additional decade of fantastic musical reproduction! Cheers to all!   

  This makes no sense. The Citiscape line is a step below the Fidelios.