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(Edit) I have the m50s, not enough bass.
This.
Now... there are a few vintage headphones that are an option. The KOSS PRO/4AAA (not to be confused with the current production PRO/4AA or PRO/4AAAT) has the absolute best bass I've ever heard in a headphone, it's almost speaker-like in the sense that it'll slam the hell out of your head and has this immense presence to it. They isolate almost perfectly and have absolutely INSANE build quality; these things could probably survive being run over. After modifications the headphone can even compete with headphones in the $400+ range like the HD600. Check eBay, they usually go for $50-80 or so.
Keep in mind this is not without its sacrifices. The 4AAA in stock form has a kind of crunchy sound that works well with metal and electronica but not so much with some other genres. They do have recessed treble as well. But the main sacrifice, while not an issue for me, is the comfort. They are EXTREMELY heavy (LCD-2 heavy, 530 grams) and have these hard, pressed vinyl-type earpads that seal perfectly against your head (hence the insane bass and isolation) and cause sweat buildup. I've never been exceptionally sensitive to comfort in a headphone but others tell me the 4AAA is one of the most uncomfortable monsters they've ever worn.
They're also <BIG> cans, they stick out from the head quite a bit. Personally I don't care what they look like on my head if they sound good, but you might not want to wear them out for a walk. If you want a portable, the HV/1A from KOSS uses the same drivers as the 4AAA, but tuned differently and with foam pads instead. They're a bit rarer and prices can go crazy though, and I haven't actually
heard it so I can't give a complete analysis of it.
But really, give the 4AAA a try, if it's not for you you'll find a KOSS fanboy somewhere who wants to buy it. Maybe me?
Now, just a warning, if you DO choose to try the 4AAA, be careful. There are three revisions of it, one of which is a black sheep with a redesigned (terrible) driver and considerably worse build quality. Look at the baffle for a concentric pattern on the acoustic lens, or alternately look at the hinges on the yokes. The following pictures show the things to avoid.
Good luck!