Difference between Digital Output, Speakers, Digital Output (Optical)

first: do keep in mind that the m50x is a "bassy" class headphone and not a "bass cannon" class headphone so there is a physical limit to the amount of bass it can produce compared with other models.

no, actually the m50x are fairly bassy and are not balanced at all. its a v-shaped sound profile (subdued mids) with more emphasis on bass than treble. something like the hd598 would be considered balanced. this is why its in the "bassy" classification. with that said, if the m50x isnt doing it for you then i'd suggest getting into "bass cannon" grade headphones although keep in mind that going this route means you will lose the subtle details in treble and overall things will muddle up a bit.

with that in mind you can manage to squeeze a bit more bass out of them by using EQ settings or using an external amp with a bass boost feature such as the e6 and similar have (this is basically the exact same thing EQ does though). if boosting the eq / bass boost is not enough to satisfy you then yes, you need bass cannon headphones.

something like the dt770pro-80 is a bit more bassy than the m50's (though in the same "bassy" classification" but given that these dont seem to be enough for you , i would warrant that you wouldnt be happy with these either.

*unless you feel like spending pretty hefty cash for a hifi-low-end boy class headphone. typically you're talking $300+ for something like a denon d2000 and similar.