I didn't see this post as it was in the wrong section on the forum....anyway, as said above.
Through the bulkhead on the passanger side of the car, then down under the carpet and into the wiring run on the passanger side. Take the glovebox out for easier access.
I never knew In Phase did a 900wrms sub and amp though, where did you purchase it from? They are quite blatant copies of another audio brand!
For anything over 1kwrms, 0awg is preferable. However, 8awg for 900wrms is definitly NOT. Maybe over 10cm, not not 3 metres....
4awg for 900wrms and normal use should be fine though. Make sure it is at least 4awg!
I need to update my sig, I'm now running over 2kwrms with 0awg cabling.
Btw, 0awg isnt 'that' expensive. a 0awg kit from Car Audio Direct is just over £50, which is very good price.
Oh, and no, power caps do NOT help. Read the FAQ/Tutorial post in the ICE section of the forums.
You'll want to do 'the big 3' upgrade if possible. A bigger battery would be better also.