[Q] What app(s)/method(s) should I use for syncing music across many devices?

I want to thank anyone who answers this in advance. I am usually pretty good at figuring this stuff out but at this point my head is spinning.

I just bought and Asus 300 tablet for house use. I mainly bought this for our 4 year old for learning apps and entertainment. I then realized that I have her music on a bunch of other devices so I figured that now would be a good time to get everything synced up with one another. I am mainly concerned about the music aspect of syncing and if an app(s)/method(s) included other things like pictures and videos I would not be opposed. The main devices I want to sync are as follows:

2 galaxy s3’s

2 older Android phones that will be used as media (music devices like an ipod) which are a Epic 4G and a Evo

1 Asus Transformer 300

2 computers running Vista and Windows 8

And maybe if it wasn’t a problem an XP desktop, an XP laptop, and an Ipod nano.

The nano is not a big concern since I know how Apple is about sharing and I could just take most of my music to another system/use another method. I have looked into Amazons Cloud Player and have heard about some other Apps like Double Twist but I am still a little lost. I am basically looking for something that is more or less fully automated (or pretty close to it).

Thanks in advance,

Jeffrey