I feel like it would be courteous of you to turn down the music at least a little bit if the volume is truly affecting your neighbors.
While it may seem odd that they are just complaining now after 2 years or so of you doing this, that really may be the case. Then again, the wife might have just recently starting having the headaches and your music is the easiest thing to target, so that might be what they're doing.
I would suggest looking into it before you do anything rash.