From my understanding of Coustic amps, they are slightly under-rated. Even at that, unless you're really pushing the amp hard, I wouldn't think that it's pulling more power than an 8 guage can handle. What are the internal fuse ratings of the amp? IMO, you are borderline for needing a 4 guage power wire. On the other hand, you would only benifit from stepping up to a 4 guage. So what I'm trying to say is that it is not necissary, but it wouldn't hurt.