Put a screen door mesh over them and call it your old plasmas. :P

From the listening positions sit down and have someone take a mirrior and move it along the wall. Find the largest area that will look nice that you CAN NOT see your main speakers from. Those places you can see your mains from are trouble makers regarding sound reflections. This way you can put what looks best over your posters with minimum sound problems.

Read a lot about this stuff lately.