In reply to:

How about using 4 bricks under each speaker? Lay out 2 going let-to-right, then lay anoter two going front-to-back (for stability) under each.

I think that I'm going to do just that.

In reply to:

If you want to get something that looks better, you could consult with a landscaper and ask them to get you some nice stone pavers.

Well the bricks that I would take are from the street (lol), but they don't look too bad imho.