Yes! Momentum are really pretty bassy in comparison and more suited for hip-hop and pop, but not aggressive enough for rock or quite detailed in the right regions for classical. The Sony's sound better than the AKG's without any sort of an AMP/DAC...An amp makes them louder, but also brings out certain details in them that gives them their tremendous depth. The AKG have a low sensitivity, meaning they need a bit of voltage to really sound their best, nothing too flashy but something minor and clean.
If you're not going to be using an AMP/DAC/Soundcard at all I might look into the Soundmagic HP200 or Fidelio X1/X2 if you can't find the Sony MDRMA900 for cheap
There are also some good closed options: Yamaha MT220, NAD Viso HP50 Brainwavz HM5, M-Audio HDH50. or maybe those new Rock Jaw Acero
....Those all sound really good without any help.
I like these a lot more than HD-280, and they isolate nearly as well, and are so damn comfy
http://www.amazon.com/dp/B0093PVTPS/?tag=neogaf0e-20