If the headphones' impedance is really low, then the amp could potentially run out of 'juice,' leading to a weak, thin sound if your amp isn't strong enough to put out the current needed. That alone won't wreck anything, but if you crank it to try to get more volume, it'll distort, and that's what wrecks the speakers.
That being said, 64 ohms isn't really that low. My AKG K271s are 55 ohms, and they work just fine through a portable CD player or Edirol UA-25. Start quiet and slowly turn up the volume, and see if it distorts before it gets to the volume you want. If it does, then you'll probably want a dedicated headphone amp. If not, I think you're good to go.
As for it leaning to the right, I don't really know what to suggest there. I've had strange audio issues at very low volumes before, but they were amp circuit issues like the left channel ramping up slightly before the right, which was significant at that volume.