I've got the 70 inch Grand Wega built into a wood wall unit. I'm on my 3rd bulb within a year--the thought is maybe it's the heat. ( I understand the newer models have an additional fan???)

I've got some space above toward the back of the TV in the unit to drill some 2-3 inch holes, but I think a fan(s?) would help-- It needs to be really quiet and plug into a regular a\c outlet (or have a brick adapter).

The fan will sit behind some speaker fabric and in between my l\r\c speakers that are above the tv.

Thoughts? Suggestions?

I would use Active Thermal Management. They have a couple systems that might work perfect for you. The nice thing is they have systems that increase fan speed when the temperature rises and they are very quiet.

To cool an enclosed unit you need to move enough cool air in and warm air out to keep the heat source for gaining on you. Moving air around inside a cabinet will not do the job, and may actually add to the heat load by the amount of wattage consumed by the fan itself.

If you are going to move air through the grill cloth you can expect it to get dusty over time. Drilling holes may or may not help, depending on where they are drilled. Keep in mind that heat wants to rise, so see if you can arrange a cool air intake below the heat source and a warm air exit above. Without both of these you will just have the same trapped bubble of warm air you have now. Small holes mean you need a fan's help, large holes (read: very large) mean you may be able to count soley on convection.

IF you have the space above the TV in the LCR area, make a Fan box out of 1/2 MDF and line it with dense fiberglass or Jute material (carpet pad). Place 2 fans in push pull configuration inside the box isolated on rubber or neoprene spacers. 12v computer fans will be fine,and use a 9v adapter or 6 volt adapter for lower speed if you still hear noise. place this box on top of the holes you have cut in the shelf for the intake. The exhaust can go into a small S shaped 4" fiberglass lined duct to reduce the noise.
buy a cheap (>$10) thermostat and place the sensor in the top of the TV cabinet. Have the Client take a look at it after the TV has been on for a couple of hours. Do this before and after the fan installation to efficiently measure your solution.

You can plug the wall wart adapter into the A/V reciever's switched outlet or buy a cheap thermostat and wire in series with the power supply.