You can set up Gmail (on their web site) to "collect mail" from Yahoo, making it available in a separate folder (Gmail calls them "labels").
Then you can also set up this Yahoo mail address as an address for sending, also on Gmail's web site, in settings -- so you can reply to those messages and the recipients will (mostly) not know the difference.
And if you do that, you'll be able to add the @yahoo as an identity under your @gmail in AquaMail as well.
There is a user written help guide on this kind of set up here on the forum, it's in "pinned" (top) messages in one of the forum's section.
