First question is: what is your budget?

Second question is: What do they like? Just because you like wine over champagne does not mean they have the same tastes. In my experience, non-wine drinkers will prefer sweeter and more approachable wines as opposed to a wine lover's "good wine".

Third question is: Do you expect them to take the wine back to HKG? It may not be the most security-friendly gift.

I think it's hard to go wrong with champagne; the symbolism is appreciated even if the wine chosen isn't perfect, or the couple are not 'wine drinkers'. If you have the budget, go with a big prestige name like Dom Perignon, which usually comes in an impressive gift box. Otherwise, choose a $20-50 bottle from the grocery store. Check Sam's Club or Costco rather than red envelope for a price savings.