I called CX, and they told me that we can't just buy an F fare for the sector- we would have to upgrade the entire trip to F

We just wanted to have F for one of the sectors, so my wife could try CX F. I've used it before, and we've both used SQ F a couple of times.

Upgrading the whole trip makes it too expensive at this time- 3x more each, so I'll wait until I'm in HKG, and ask at the lounge or the transfer desk. If the quote is too much, then we'll just have to suffer in business class