Difficult Music should mean the music is difficult to immediately latch onto. It’s difficult in the way that a knockdown shot using a 5-iron through 75 yards of trees, running a remaining 80 yards up to the flagstick is difficult. You may have to try it over and over again, and it will be difficult to do, but once you understand it, it’s that much more rewarding. Just like the feeling you get when you’ve made that incredible golf shot through the trees.Personally, I didn't have to listen to BHS more than once to be completely taken, but I can see how other people might need more time to bask in their weirdness combined with brilliant musical combinations.
The author gives other examples of difficult music that winds up being rewarding - Bob Dylan, Tom Waits and Captain Beefheart all fit the bill of music that is very different from the status quo, but in the end, hard to stop listening to.