Which one of these should I go with

[Scitesh]

My current setup includes 

Audio-Technica m50x

Audio-Technica ad 500x

Sennheiser 461i 

Sennheiser 280 pro (old version) 

And I'm planning to add/upgrade these 

These are the options that I am confused bw

 

1)Sennheiser 6xx/used 650

2)Sennheiser 58x/used 600

3)(combined deal) Sennheiser 598se+audio technica M40x + Beyerdynamic custom st

4)ultrasone 840

 

[Jz1]

HD 600 is closer to a neutral sound. It doesn't have as much bass as the 650, but the high frequencies are not as rolled off or 'veiled' as the 650. Typically, the 650 is a bit more expensive than the 600, so its usually concluded that the 600 is a better purchase. Also considering that you have headphones that are already bass heavy, I would opt for the 600 sound. The 650s have a wider soundstage and would be better suited for gaming. They both sound very smooth and can sound boring. although the 650 is slightly more coloured, it can be more interesting than the 600. Neither are wrong, it depends what your sonic preference is.