Stereo upgrade.. n00b needs help

Just completed some system upgrades for my '01 SAN and tried it out. I'm stoked about the potential, but have some problems. Both in the garage AND while the engine is running I can't turn it up to any signficant volume as the amp goes into "protection" mode. What I've done thus far is:

Sealed sub enclosure with 10" Kicker sub, dual 4ohm voice coils wired in parallel.

Kicker 700.5 running boat speakers (upgraded interior Clarions to Sony Xplodes) and sub. I am 90% sure I've got plenty of power to run the sub.. it isn't a mega high-powered job and I giggle at the thump it already provides at low volume. MUCH better than my stock stereo. I'd like to be able to turn it up, tho.

I'm running 4 guage wires, both power and ground. Power is directly to the battery (low-end interstate battery, which is probably barely adequate) and the LONGISH ground (~9')is connected same place as my engine starter ground. I went there instead of directly to the batter to save a few feet.

I'm thinking first thing to try is a stronger battery (Optima Blue Top) and maybe should be running two? It's NOT a powerful system and I wouldn't think a 700W system should tax a single battery. Anyone have any thoughts what might be causing my my low-volume issue? Maybe the sub should be wired in series instead of parallel so it's running at 8 ohms?

I don't think you would want to wire it at 8ohms. The amp can handle a 2ohm load according to their website. Are you positive you have a dual 4ohm sub and not the dual 2ohm?

Did you get a good ground, meaning no paint or anything between the metal? You can try the ground on the battery to see if it goes away.

Yeah, good call on the ground as I think I might be able to stretch it a couple extra feet to the battery. That's one thing to check as I know grounds can be finicky.

Now you have me 2nd-guessing myself on the sub. I was assured it was a dual 4ohm, but now I guess I should double-check that. Looks like I've got a couple things to check here, the sub doco being first on the priority list.

Its got to be teh wrong ohm load. If your amp is going into protection mode, you working it too hard.

Have you tuned the amp? You can change the gains on the amp to significantly change the volume.

OK, going for hopefully the easy fix I pulled the sub and checked it... definitely a dual 4ohm sub. Argh.. I guess that gets me back to checking the ground out.