Although the 747Adv and 773ER are favoured, as SMOC says, don't rule out Airbus fighting very hard for this one. If rumours on the Dunnunda/Godzone section are correct, they've lost QF, which is expected to order 773ERs. With SQ also under the 773's belt, this makes CX a "must win".
Another factor is the 747ADV; although CX is clearly interested, how many other carriers are interested in the pax version. There are quite a few interested in the freight version, but will CX's interest on its own be sufficient to launch the -400Adv pax model?
As part of any CX deal, Airbus would presumably take back the first three 346s and replace them with -600ERs. A further factor in Airbus's approach would be that CX is the lead carrier associated with the pax version of the 747Adv. Sign CX up for the A380 and Airbus has effectively pulled the carpet out from under the new 747. And if it takes cut price A340-600ERs as a sweetener, then so be it ...