It IS sound! I am quite sure Qxa8 is the right move there. If not you would just be losing the whole bishop!
However, you must be careful not to neglect your own development (castling, your queenside pawns and pieces) and the position of your queen since black's bishops can become very effective and develop easily after Qxa8. Perhaps you can share the rest of the game for people to comment on 
I currently play in a tournament, and in one of my recent games someone played cxb5!? here:
Not having seen this move before, I did what I thought was the logical move (Qxa8), but I played badly from here on and eventually got my queen trapped. Is this sound, or just a very complicated line to catch people who are not expecting it?