I have had good luck with LED strips. From the picture, I would attach it higher on the back of the light box area, facing forward. It looks like it would clear just about any speakers that way, and there is more than enough depth to diffuse the LED light and backlight the marquee evenly. The only thing I would consider if you go LED is adding a PWM dimmer so you can dial it in to the right brightness, those LED's are bright and sometimes too bright. If you did end up with a shadow, it would be easy to move the led strip or add a couple more segments in other places to fix shadows.