That's a conversation the Democrats keenly want to take into the next debate. Ryan was faced with a question of how his team could possibly make 2 + 2 = 6. And he continually said, this is something we'll leave to good faith bipartisan compromise. But this makes no sense. This question isn't just a matter of idle curiosity. The reason people are pressing for details is that the math simply doesn't work without big tax hikes for middle income earners. But Romney and Ryan don't want to admit that.
It's clear that the whole closing loopholes explanation is just a tack on to get through the campaign without explaining how the numbers work. You don't need to go further than Romney's own website. The section on taxes just talks about an across the board 20% cut. There's no mention of closing loopholes at all.