Too much bass on electro music will make u get nausea. But yeah, no point really in having an amp for your ipod. I mean, theres a difference, but the portability loss and the price isnt worth it. It's very cumbersome to walk around with a long LOD cable, rechardgable batteries and all that. If you want to use them with your PC u will most likely get distortion without a DAC, having an amp without a DAC wont make it any better, probably worse, but if you're going to buy a DAC you're also going to need an external amp. And then of course there are combos. D4 mamba or D2+ boa is the first that comes to my mind, but there are also some cheaper alternatives around 100 bucks like the m-audio transit which i believe has an integrated amp as well.
www.ibasso.comM-Audio Transit USB | Sweetwater.com
Both the D2+ and the D4 have integrated amps. Remember that they can just be run from USB, and not optical or other digital formats.
But seriously, hear me out on this, what's the difference on buying one now, and one later, instead of buying two at once and realize it really wasn't worth it. Either way the HD 25 is very portable, and when u start to climb the price range, you wont be that portable anymore.