Yes, you can fit x2 560s in the bottom chamber, though plumbing is hard! Top chamber can only have 480s. 560 in bottom chamber means removing front intake fan, which I have done. Just done my first sleeving ever, on a GT fan. Looks ok. But now you've intrigued me with the soldering idea!
I was planning on pulling air in on front intake, and pushing air out of back of case on rads in top and bottom chamber. Does that sound OK to you?