After trying to heat my house with a fireplace like yours I put in a Buck stove.  What a difference it took less and 1/4 of the wood per day and heated the entire house (sometimes too well) where we were not even keeping the living room warm before.

Just an little bitty tippy.

I have a heatilator masonry metal firebox similar to:
http://www.yourwayfireplaces.com/docs/Air%20Circulating%20Metal%20Fireplaces.pdf

I can heat 1/2 the house with this unit and bring the temp up to 75 degrees in no time.
If you were to place you hand in front of the top registers, you'd singe the hair off the back of your hand!

I was contributing to this thread:
http://www.fieldlines.com/comments/2007/11/20/122831/20/25#25

The one feature that you MUST have besides the glass firedoor, is an external damper control so you can shut down the burn rate and increase the heat in the box, and prevent more of the heat going up the chimney.
Without it, you have no means to open the closed damper when the fire is burning and keep smoke from filling the house when you first open the glass doors

You are on the right track as far as blowers....you need a means to extract more of the heat and there is a very simple implementation .....get two of the 115v 4 inch box mini fans similar to the 12v kind in a puter case. Place them just inside the bottom intake grates blowing in. If you can find surplus (or eBay) 220v units, hook them up to 115v and they run at 1/4 power and are noiseless.

There is no magic in a wood stove or insert ..they simply have the means to control the burn rate, limit the air intake ....my problem with them is that their capacity is too small ...I burn five 24 inch split logs at a time.

From your pics, it doesn't look like you can change very much ie add registers on back side towards hall, but if you heat up all that stone, it will radiate in all directions for many hours