Midgetguy
Headphoneus Supremus
got'em!
i haven't had my 598 for over a year so i'll do my best to compare.
plugged into my receiver; yamaha htr 5550 headphone out (it's all i got for now) i have to say i was let down - which i expected, given that it's a headphone out.
so far it sounds like a 598 with better detail retrieval overall, solid mids, better bass quantity/quality and a MUCH smaller soundstage. there are a couple electronic songs i enjoyed on the 598 that give me a surreal "out of head" experience. i didn't get that with the 600. there's some instrument separation, but i don't feel it's worth mentioning above any other average headphone. one thing that was nice, however, was that i found a lot more texture in electronic music i had not previously heard.
one thing that immediately became apparent is that my description of "lush vocals" for the 598 really should have been "forward vocals at the expense of everything else". the 600, while sounding perfectly average in stage/imaging, sounded better on all fronts except maybe the vocals. they still sound very good.
sorry i can't be more specific; don't have that critical of an ear yet - but it's natural, it's laid back. all parts are present. i have a feeling a decent amp is gonna bring this way up and blow the 598 out of the water.
if i had to choose right now? i'd prefer a 598 unamped over the 600 unamped, despite the improvements. the soundstage and imaging are the reasons why. when i wore the 598 i could forget i was wearing headphones - i felt like i had instruments playing all around me, like i was on the stage behind the band/people/whatever, not like i was in a concert hall. thankfully i'm not going to be keeping these unamped.
i've decided to start small and simply use the 150$ amazon gift card to get a starting point - a couple reviews pointed me to the asgard 2 as a good place to start despite not being a tube amp. would this open up the stage and imaging while keeping the largely neutral/natural characteristic of the hd600? many reviews seem to indicate such. i'm thinking later on i'd spring for the mjolnir 2 as my "endgame" amp after i've saved and learned to enjoy a basic amp and dac.
This is one of the noted strong suits of the HD600s in my opinion. While it may not necessarily blow you away (the wow factor some people look for when expecting an upgrade), it really doesn't do anything wrong. That's what has made it such a legendary headphone. Pure performance, no gimmicks.
You could very well be correct about the issue with the issue of amping; The HD600s are 300ohm headphones after all, while the HD598s are only 50ohms, making them much easier to drive.