Talked to PAC today, they have a solution but it's not an easy one. Here's what he had to say:

Unfortunately we have not had the time to update the 2003 Infinity system as of yet. We are aware that the harness is different though. If you are looking for an integration piece, our universal OEM-2 will work just fine.......but is NOT Plug and Play. So a strong installation background is critical.

So I asked if/when they will have a 2003 infinity harness out. He said:

Unfortunately, we have no plan for a new production just yet. But, if I had to guess, I would say early spring if at all. Sorry.

So we can either wait and hope, or switch to the OEM-2 which is universal, but not plug and play. I've got to give it some thought, but I am pondering going with the OEM-2.