L;
Let's eliminate any problems with inadequate 12V wiring first. Your existing battery, if good, should be able to give 48-58 Amps for 12 minutes. I know an AGM battery will do that.
I didn't suggest, but said that I use two 3' sections of 2/0 cable. Including a 250A fuse, it is 7' round trip. I can do this short run because I use an aux/house bank to power the 1000W inverter. I only needed 3' sections to handle the bending radius. The inverter is about 6" near to the bank.
My 1000W Magnum inverter recommends a minimum of 1/0 for 3' to 6' one way. I kicked it up a notch and got 2/0 cable since 6' was right on the borderline.
Your manual says "Note: Xantrex recommends a size 0 cable with a maximum cable length of 6 feet (1.8 m)". Sadly they don't say if that is one way or round trip! :( Plus, where do they get off with 0 gauge with inverters from 600W to 3000W. Now that you have a 2000W inverter, it is wise to cable it for that amount. Of course, you could use the Voltage drop table, but what is acceptable drop?
The goal is short 12V cables and let the 120V be the longer run.
Can you tell us what the one-way cable length is between the battery and the inverter and what gauge you are now using ?
How close can you get the inverter to the battery?
HTH;
John