You can compress it as long as you keep the quality high. Mp3 compression only strips extreme high and low end frequencies, which you won't be able to hear anyways.
The point of binaural beats is for the brain to create the 'third tone' by subtracting the low from the high frequency. It doesn't matter if you hear it or not, the brain does process it. If you clean the highs and the lows you remove the binaural aspect, and you're no longer doing hemispheric synchronization, you're just listening to repetitive beats, which is not why you spent the money on binaurals.