Good Audiophile Headphones?

what kind of a sound profile do you want?

those two headphones are more focused towards highs and mids with rather recessed bass output (although the 558 does have a bit more bass than its bigger brother the hd598 but a smaller soundstage, the ad900x however is better in both ways than the 700). the 558 however does have more bass than the 700 which is almost nonexistant.

spatial positioning is better in the next step up in both models (hd598 or ad900x) as well however the two models you picked are not bad at all but lack just a little bit of the clarity (naturally since they are cheaper) of the next step up. good for the price though. due to the limited bass the ad700x may have more "simulated positioning".

they will work well for gaming and music provided you are not a "basshead" in any way shape or form. if you are, you might find the bass output a bit light on the 558 but nonexistant on the 700

both are said to have a warmer overtone to them.

you can read a comparision here http/www.head-fi.org/t/628057/newbie-looking-for-help-senn-hd558-or-at-ad700-for-gaming-low-budget where someone else was thinking about buying one of them.

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honestly without you listing your preferences as far as sound is concerned its hard to say what exactly may fit you best.