[ganroxex]

I wouldn't hold my breath. Had mine for a year, I love them but no they're not bass heavy. They're very light in the low end but I like that. I don't know if it's my pair only or not but I've felt a huge difference in bass depending on the source. off my phone or laptop the bass doesn't exist basically. I usually use my dragonfly black and that makes it a bit deeper but you can tell it's still not strong. On my panasonic or Sony home theater receiver however the bass is much much stronger, while still being controlled. That said, again, these are not bass heavy headphones so no.
As for the K7XX I've never used them but from what I've heard and seen they're slightly boosted in the bass and have a much fuller low end. They're more analytical though, more accuracy over everything, like all AKG, but with bass. while the 598 sounds like usual senns but with (a bit) more highs.

I've known from reading several posts that HD598 has a recessed bass, but I never imagined it to be quite so....reserved in comparison to my other cans. It is my first headphone of sennheiser signature, loving it on any other song which is not dominated by bass and subbass. 
 
Glad to hear that K7XX seems to be balance out in the bass department, I'll have no reservations next time I see them on massdrop, thanks!

 

[447563]

I've known from reading several posts that HD598 has a recessed bass, but I never imagined it to be quite so....reserved in comparison to my other cans. It is my first headphone of sennheiser signature, loving it on any other song which is not dominated by bass and subbass. 

Glad to hear that K7XX seems to be balance out in the bass department, I'll have no reservations next time I see them on massdrop, thanks!

What are your other cans if you dont mind me asking? As for the sennheiser sound, it obviously changes from line to line but they generally have rolled off highs to make them sound smoother and more enjoyable. Great to reduce ear fatigue but not for analytic hearing.akg don't do that. The 598s have a small bump in high miss and are shinnier than usual but still not too much.as for the K7XX it's more of a slight bump than neutral in the lows

 

[ganroxex]

The cans I own right now are Momentum 2.0, Beyer T51i, and Sony MDRXB-950. They are all closed cans with some emphasis on bass. I know that with the HD598, its open nature will sacrifice a lot of the bass for soundstaging, yet I was still not prepared for the sudden withdrawal of bass it gave me. 
With regards to HD598, I've noticed its treble being quite shiny on some of my brighter tracks, however it isn't too much of nuance to me.

 

[Brad57]

HD598 > HD600 > HD650

My tastes run opposite of price in this case.

Mine too. I even doubt there might be some difference in hd 650 variants that some people gets a different sounding unit,ends up not liking them.