As we continue this conversation from three years ago, I would like to add if you still have the factory turbocharger you are well past it's efficiency range at 7000rpm. While extra headroom is never a bad thing, you'll need a pretty serious turbo to justify taking this engine up to 8000rpm.
For what it's worth the 360c seems to be pretty readily available online at various retailers and also in stock at a wholesaler I checked with. Perhaps they have restocked since you last checked? It does have a heck of a price tag though.
A catless downpipe with the factory Si "catback" is a recipe for rasp. Adding any resonator should help. The Vibrant Ultra Quiet recommended above is always a good option.
That website has came up several times on the forum and the general consensus is that you get what you pay for. It is hard to expect a proper custom tune at that price point.
Sorry but you do in fact have it backwards.
Long story short, the ECU has to add MORE fuel to maintain a proper AFR, it adds fuel, the fuel trim is positive.
I would recommend posting a log. A datalog, not to be confused with the one you drove over. :)
I'm guessing there is not much to this but the datalog will tell the tale.