I cut a ply board 20" wide x 11" long. I then designed, on paper, how the cutouts would look.  I based it on another design I found on the Internet.   

I laid out the cutouts by starting with two circles.  I used a standard CD to trace for the circles (4-3/4").  I put each circle in 2" from the side and the bottom of each was 5-3/4".  Within that I laid out the pattern in picture 3.  I started each cut with a drilling a 1/2" hole at each end and then using the jig saw to make the straight cuts. 

I also cut the two boards for the marquee, which are detailed on the next page.

Next I sanded it all, including inside the cutouts.  I then tacked it off and primed both sides.  I painted the inside of the cutouts from the back side first.  I gave the back a real quick swipe of paint as it will never be seen.  I painted the front with three coats, just for the heck of it as it took me a while to get the inside of the cutouts looking good.  [I painted both sides of the other two pieces, two coats on the front/top.]

I then cut two pieces of fabric (actually a black bed sheet) and stapled the pieces to the backside of the board.  I then screwed in four cuphooks, for the wiring to loop around.

Then I, very elegantly, strapped the speakers down using some spare speaker cord I had laying around and a little electrical tape for good measure.  I made sure the on/off button was extended into one of the cutouts so it would still be useable.

I then attached it to the cabinet by screwing four screws into the ledgers found on either side.  From the playing position you cannot even see the speakers.  The fabric keeps them totally invisible.

There are two protuberances on the left speaker, the volume and the on/off.  The on/off switch can still be used as it is a simple toggle.  The volume can now only be adjusted through Windows.  This is not a big deal. 

[Update- I tried using Velcro for some customer cabs.  I bought some 2" wide, black stuff from Lowes (sorry for the Staples link). I attached a strip to the top and bottom of each speaker 'grill', in the cabinet.  I then cut two strips of the opposite half of the Velcro and attached to the speaker.  Then I simply attached the speaker inside the cabinet.  The angle of the speaker area is very shallow so the chances of the speaker falling are pretty slim.  This method turned out to be much better than strapping the speakers in place.]