Well, the first step is to diagnose where the problem actually lies... if you are using the usual red/white RCA connectors somewhere in your chain, just swap them temporarily. Then listen: are the voices/music switched as well? If no, or for instance the voice that used to be full left is now almost centered, but not full right, it may indeed be a hearing imbalance. If yes, then it's most likely not your ears but the chain and/or recording.
Actually, most likely the recording. You can find test sounds/tracks that play full left/right. If those sound correct, then it's the recording.
If not, one more test of your equipment chain is to try to play back a mono recording (be sure it is!) like somebody else suggested. It should be centered. If it isn't (properly centered, or full left/right), try removing each part of your chain. Example: plug the headphones straight into any other source (laptop, CD player headphone out, MP3 player etc.) If they sound fine, try your amp using an analogue source, leaving out any DAC you are using and so forth.
The important thing is to do check one thing at a time, it will be more time-consuming to narrow things down if you change several things at once, or just use a variety of music tracks which may all have unique left/right mixes that are difficult to clearly nail down.
As far as hearing imbalance goes, have them checked. It may be as easy as having them cleaned (carefully!!) (also:http://www.head-fi.org/search.php?search=ear+clean)
Edited by TheGrumpyOldMan - 3/20/12 at 1:53pm