32ohm vs 250ohm vs 600 ohm headphones, need help on choosing Options

[aaronius]

Ok, I'm just getting my feet wet into this audiophile stuff. But, I love my music and want to hear in the best way possible that I can afford. I have found a really nice pair of headphones that fit my budget.
However, they come in 3 different OHM's. I can get the Beyerdynamic DT 990's in 32 ohm, 250 ohm, 600 ohm. From what I understand the 32 ohm doesn't require a seperate headphone amp
and can easily be driven by a pc or mp3 player. (I'll mention that all my music is in AAC 256kbps. Not quite lossless but still much better than standard 128 kbps mp3.) But the 250 ohm and 600 ohm do need an
amp to get the best out of them.

My questions are:

1) how much better sounding is the 600 ohm over the 250 ohm over the 32 ohm? If any?
2) Will an inexpensive headphone amp like the Fiio E7 or E11 drive the 250 ohm enough to get the sound I paid for?
3) I plan on using these on my desktop computer for music (rock/metal) and gaming. Am I better off with the 32 ohm or is it worth the extra expense to get a cheap amp for the 250 ohm?

I appreciate the educated feedback as I am a complete noob and need help on this.