How often to apply wax,to cabinet?

Wax, once applied, doesn't go anywhere unless removed by friction or abrasion. No need to reapply as far as the protective aspects go unless you're rubbing it off somehow. I would not agree that wax is the ideal panacea for wood care. Veneers can dry out and delaminate. I have been of the opinion that keeping room humidity levels high enough is more important than any waxes or oils. If wood veneer becomes dry, an oil purpose made for remoisturing wood is a good option.

Does any wax or oil actually penetrate for moisturizing into wood that has been laquered or varnished?

When building a cabinet (I'm a woodworker) the adage goes: "Once a day for a week. Then, once a week for a month. Then, once a month for a year."

What kind of confuses me is wax over laquer. With most laquer finishes - think of piano black - applying wax over laquer would only dull the finish. Assuming that your speaker cabs look better for having done the wax job previously, I'd say go ahead and do it again if you think it needs it.

Wood moves. Wood or wood veneers can dry out. The point of the laquer finish and wax is to radically slow down the process so that it takes decades instead of months to dry out (or sponge up.)

To answer your question more directly: If it's been a year, you would likely want to do it again soon.

/Rob

PS: Feel free to contact me offline with any other wood questions you might have.