hello mate
I have installed the exact alpine head unit after few weeks of wondering.
mine wasn't a bose system to start with so the decision was easier for me. I took the car around to few shops and they all agreed that an Ipod cannot be directly connected to nissan head unit.
that wasnt the only reason to change the head unit though. I had the alpine on an audi A6 prior to that. the A6 had a brilliant bose based concert system. but the sound quality had improved significantly with the alpine head unit. I didnt have to change the sub or the amplifier on the audi either to get a better sound quality.
to cut a long story short, I thing changing the head unit alone should improve the sound quality. obviously if you want more out the audio system you could change your amp and sub.
The alpine head unit you have is very strong and could deliver superb sound if you upgrade your amp and sub as well.
having said all of that, The US 350's bose head unit could be connected to an Ipod directly I think. (some 1 correct me if I am wrong)
I am not entirely sure which diagrams your after. clarify a bit more and I might find them some where.