My VSA speakers are already as inert as it gets but the Velodyne Optimum 12s have a pretty lightweight cabinet so adding 30# to the cabinet as I've done can't but help with any resonance issues. The Optimums are known for their accurate bass already and I feel this has made things even more accurate...punchy..etc. With shipping the bricks can be had for about $40 each.
Good job. But with all due respect, you're really missing the performance boat here. If, and I don't doubt you, you're able to hear improvements with minor mass-loading efforts on your already heavy speakers and sub, wait until you try it on your lighter more sensitive components. Remember that a feather is far more easily excited by mechanical vibrations than a concrete block.
And by all means why stop at 10 lbs.? Try 40, 50, or 60 lbs. You should notice some reasonable gains immediately but as with all things mechanical there is a settling in time so you have to be patient. If you try this with your components, make sure you bypass your components' stock rubber footers by placing metal spikes, cones, points, pucks, or maybe even some extra lug nuts.
Below is a pic of my early days of some mass loading experiments. It may look silly, but there was rhyme and reason to my madness over about a 9 month period of time until I completely saturated the components' top plates with weights (mass loading). I used whatever metals I had on-hand as you can see here.
Not only will your bricks damp / minimize the top plates' potential to vibrate in sympathy with vibrations already captured at the chassis (making a bad situation worse), but the mass loading combined with the metal objects between the components' bottom plates and shelves will help to create a superior mechanical conduit allowing mechanical (vibrational) energy that normally remains trapped within the components, will now possibly have an expedited path to exit the components before they start to dissipate within and induce their sonic harm.
I can assure you, whatever results you obtained at the speakers will pale in comparison to whatever you try at the components.