Many cheap phones I've had and helped friends with, have actually been able to reproduce more sub-bass than what seems. They are nowhere near flat, and seem to roll off into silence as high as 100hz.
If you plan to avoid equlziers, you won't really get sub-bass out of nowhere.
An amp will help push the relatively large amount of power headphones need when they work like this, and I actually can't say anything about how safe this is for them. What I know is that DC hurts or kills headphones (according to someone 0.1VDC into grados over time will damage them).
The eq curve in foobar (best standard non parametric I see commonly and easily integrated for others) end up being at +0 for the 55, and quickly drops almost to -20 by 220hz in some cases depending on how much the person wants. Essentially, don't boost the bass, but lower everything else, and crank the volume to compensate. The bass fraction of the music will be coming out of your headphones as if you had the volume turned way up. Again, I don't know how harmful this is but I have yet to break any phones and they are not clipping.
My avatar is actually roughly the curve I use right now for some low end phones (xd400) Check how large the drop is from bass-mids. The rise in highs is actually because I have this ridiculous sensitivity to mids in audio, not cause I'm trying to forge bass. Headphones, even HD650's, all sound way too MAAAAAAAAAie, like a mid-range speaker without tweeters or woofers. This is a flat speaker system I am comparing to. I think the earlobes of certain people can be shaped to be extremely pronouncing of certain frequencies, depending on whether the sound is from phones or elsewhere in the room.
