Alright, this has gone on long enough.
It's quite embarrassing that I don't know such a basic piece of grammar, but somehow I've never learnt it, and no matter how much I hear it, the only thing I can guess is that it adds feeling.

What does the grammar ~なんです mean in the context that the Japanese put it at the end of nearly any sentence.
e.g.
好きなんです。
そうなんですか？そうなんです。

http://guidetojapanese.org/particles3.html#part5

That'll give you the basics. Other than that it's mostly a matter of just seeing how it's used, which is easy enough since it's used all the time.

Ah, I thought it might have just been な　＋　んです。
Thanks.