How to sync music to iphone from another itunes account and library

I was killing myself trying to find the solution.

I use iphone with a lot of apps and old laptop as my syncing library.

My wife is a newer iphone user, and her main desktop PC is her base. As well as base for our music, movie etc purchases and it is homeshared and played by whole family.

My problem was going on a trip and playing my 4 albums from my old library for ages - I got fed up.

I wanted to use music that I payed and downlaoded to her PC.

Friendly apple care guy told me that I can either

1. sign out of itunes account on my iphone and use hers to log and one by one download all her music from the cloud, while retaining my old music on my iphone (which I dont want to hear anymore!)

2. sync my iphone (after backing it up and transfering purchases just in case) with the MUSIC TAB on my wife's PC's iTunes library (use only music tab will sync only her music and not erase everything from my iphone!).

I am opting for second and hope it willnot erase my voice memos and programs and files. If it does, Ill just restore from backup.

The apple support guy was fantastic!