The project is now successfully completed. Carpeting was done by a local shop that carpeted our house. (installation was cheap enough that it wasn't worth the risk to me of having an ugly installation that the wife would comment negatively on). The rest of the work was done between me and a friend and turned out very well (IMHO). The only thing I'm waiting on now is the arrival of the new chairs to sit on and in front of the riser.
Below are a few pictures of the construction - several more are available under the link in my signature.
Initial framing with 2x10s
Added 2x4 bracing around all edges to secure 2 2x10s on top of one another 
Cross sections filled with insulation to deaden resonance and BOOMY bass in the corners. 
2" holes cut in front of riser to allow sound waves to pass through insulation-filled riser and decrease resonance. 
Completed & Carpeted - now with registers cut in riser to allow sound waves to pass through riser and decrease low frequency standing sound waves... i.e. "boomy" bass in room corners where the riser meets the walls. 
You will probably note the registers are cut off-center. This was done purposely to provide the best combination of structural integrity and sound absorption. I will have a row of chairs sitting right in front of the registers so they'll never be seen once the chairs are put up on the riser.
I did test the riser before I cut the front 2" holes and back registers and bass in the rear of the room was truly awful.
Booming, pounding ugly bass. The kind only 17-year old with a hatchback full of 15" woofers in a homemade box could appreciate. And, since I don't have of those around on a regular basis, I decided to try cutting the holes.
The reason I tested before cutting is because I was fairly skeptical that cutting these holes would have any effect whatsoever (considering I had little to no idea what I was doing). As it turns out, however, it had a very noticeable effect and response in the rear of the room is now much more normal. It is still not as good as in the main listening position, but it's MUCH better.
I will at some point run another response sweep and post the results, but I want to get the furniture in first before going through all that effort again, so I'll report back in a few weeks.
Jason
Finally, another view of the finished riser
