That board will be more challenging to duck dive with. However despite what some of the previous posters have mentioned you SHOULD be able to do this. However it will come down to your paddling speed and the leverage that is applied to your duck dive.
First off: Timing is crucial in a duck dive. You'll need to get your timing down to know when to start getting under the wave. If not: Put some goggles on, leave the board on the beach and go flop around in the white wash and SWIM under the waves that come in....be sure to look.....this will help immensely on timing.
One your timing is down you have to focus on leveraging your board, since you can get the nose to go down fairly well focus on putting one of your legs straight up in the air right as you duck dive. This will ensure you go as deep as possible. Another technique is almost do a full pushup on the board to raise yourself above the surface of the water while holding your leg straight up vertically. This will create more momentum to dive deeper......getting deeper is key....the bigger the wave...the deeper you need to go.
If you're still having problems, make sure you're getting enough speed going into the duck dive. This will also helps with momentum of traveling through the water and can help you get under it. If this is a problem your board might be taking water in. Fix your dings, keep it in a board bag when you're out checking the surf and when you get home put it in a surf rack Like I said before the board you are using does have a lot of foam so it will be challenging. But when I was learning I truly learned how to duck dive on a 7'2" thruster that was a MONSTER. it really allows you to work on your technique to get it. You will thank yourself later on when, it's 15 foot and an outside beast comes reeling in and you get under it unscathed. Good luck and stay postive about it, remember it's a real learning process for all of us!