Sorry to hear about your KSC51. How long is the JVC warranty? Perhaps they will exchange it? Do you have any idea how it broke? Do you think the wire detached, or the driver just gave out?
How much is the Sony XBA-1?
One thing I noticed with JVC headphones is that they can change dramatically with burn in. For example, my HAS600 was so bassy and treble deficient for several weeks until it finally got
enough burn in. Then it sounded much more neutral with closer to normal bass and much better highs and detail.