They don't make the X anymore. The A20 can be had in the USA for about $990, plus duty/VAT unless you can get around that, (non bluetooth) and is reportedly significantly better than the X.
Not saying the Ebay item is bad (though it is priced right at the top of the market) but this is worth a thought.
The Bose is worth every penny and more. The best headset out there, and totally sweeps the floor with nearly all other headsets in the shops, in terms of performance and comfort for long flights. I have four of them, and have done 7hr flights without any discomfort whatever. I have just bought the A20 (did a $400 trade-in for one of my 4 X headsets) but haven't collected it yet from my friend who brought it over.
Only drawback is that if you are going to let people sit on it, step on it, hang themselves on the lead, etc, i.e. typical school/clib use, not uncommon with passengers, then get a David Clarke
(plus a bose for yourself
).