Where is Tim Cook's PR team?
They really should not be letting this stay in the headlines in the run up to their next product launch. Agree to pay, though perhaps with some negotiations, promise to be a good corporate ciitzen and get out of the headlines. Otherwise, this will still be in people's minds when next week. And, when they're supposed to be thinking "must have shiny, shiny", they may still be thinking: so 0.0005 % of the $ 900 is all the tax Apple pays?
Trying to fight this is lose-lose for Apple: it's back tax on sales in the EU that have already happened through an Irish-based tax shelter so repatriation isn't an offer and all the precedents are against appealing. Apple has hundreds of billions in cash so even this massive bill will hardly effect them. Hell, if they're accountants get them to offset share buybacks against tax, then I'm sure they can come up with a suitable scheme to minimise the actual pain.
And get lobbying for tax reform in the US: not just the corporate rate, but on taxing only where sales are made. A simpler tax system will benefit Apple almost as much as wheezes like this.