The P180 is a bit bigger than the Antec 900, but I think the cable length should be fine. I've seen it done before. I think it was decibal. He has a P180 case, and I think he used a Corsair PSU. Check the wire management thread, for pictures.
On the Corsair 620HX. It's an excellent quality, high performance, and rock stable PSU. Very recommended.