I agree with those encouraging you to explore structural issues first. Is the hood properly adjusted? Are the rubber bumpers properly adjusted (or even still there at all)? Are the front quarters securely attached?
A hood isn't like a trunk - it's not going to react to pressure changes in the engine compartment induced by your sound system. Bracing is pretty low on the list of likely solutions.
While any quality CLD will function there without problems, vibration dampers on the hood have pretty limited utility. The idea that CLDs are useful for heat control anywhere in the vehicle is marketing wishful thinking: "It has foil, let's say it's a heat product too".
Vibration dampers are unlikely to to reduce engine noise levels in the passenger compartment unless we're dealing with a high performance or large diesel engine. Even then, most noise is going to enter through the lower firewall/front floor. Noise has to pass through the hood and windshield for the hood to be a significant factor. Unless the windshield and hood form close to a right angle, this is unlikely. If it is a problem that needs to be solved, you'll need a vibration damper and then either a barrier or absorber - the vibration damper alone won't do it.
Start with the most likely culprits.
