Tablets can serve as a controller but generally lack sufficient storage capacity to be the server. Same for the SBT.
Why not get a Macbook? They'd have all you need for a competent server, are almost as portable as tablets, and far more versatile. I don't really understand the appeal of tablets - they're like oversized iphones - great when you're talking about a phone, but not very impressive when you compare it to a laptop.
Question is, what formats does Jelly Bean USB audio support? The Asus Transformer tablet pf300 is a Quad Core 1.6khz processor with 1gb ram and 8gb memory with a 32gb microSDCH card. Perfect for a music server.
2nd question is what is the best driod music playback app. I use MusicPro on my Samsung Galaxy S3 cellphone. Its amazing but only plays back flac files