Or give up on the seal and pick songs with huge bass and that are mixed loud and then audio boost them to the max. For instance Lindsay Stirling and fall out boy seem mixed loud and are actually pretty audible through water.
I really only need beat to exercise anyway.
Experience: several hundred hours of swimming with headphones through the aughts and 10s
I bought a waterproof Ipod shuffle + waterproof headphones from Amazon and it improved the experience 100x.
Note - use vaseline to seal the headphones into your ear, and wrap the extra wire under your goggle straps or you won't have a good time.
Highly recommend.