Slam is something that slams. It slams in mid bass but you don't want it stand out too much and still settle down quickly not producing secondary refraction to a point that they impact FR. Without it is dool and not very dynamic and with too much of it it's horrible and masking - leaking in the mids. How much you want depends both on SPL (psy) and material (where such peaks are present). In real material's there are two dominant DR areas low bass (mid 30's) in more bass orientated music, mostly electronic and mid bass 80 to 180 Hz depending on genre.
So for headphones it goes; closed back, good low THD dynamic drivers in a good enclosure. Planar drivers lack this ability and in order to compensate for it some of the best have boost there to compensate like DCA Stealth. I would say take a look at models with Foster driver's and more to Denon than Fostex offering (for the built quality). So you will have to experiment especially regarding fit and such however try to do it in shops or borrowing from friends until you are sure you are getting what you wanted. I use Denon AH-D5200 with EQ towards Stealth with little less boost in transition area but even those aren't for anyone (not big cups and sawing on lower turfs)... Good luck and have a good time.