What does 琴酒相壽 mean?
This is the same as 弹琴敬酒 为你祝寿, which means something like "playing the qin and drinking wine, to celebrate a loyal friend's birthday". Note that playing the qin is considered a very high-class and cultured activity in ancient China, as well as being one of the four main skills any learned person must acquire---“琴棋书画”, i.e. playing the qin, playing qi (Chinese chess), calligraphy, and painting. So the phrase 琴酒相寿 has a certain poetic or picturesque feeling to it beyond the meaning of the words themselves.