Driver selection to match bass horn

[Lars Timm]

I'm considering making a pair of these for my living room which is pretty large (50 m2):

http://billfitzmaurice.com/David.html

The low end is handled by a horn loaded long-throw 8 inch with a sensitivity of 95dB/2.83v/1 meter. It needs to be crossed over at around 150 Hz

I would like to substitute the MTM section with a fullrange driver, but don't know what to use.
The box it will be mounted in is around 11 liters (sealed).
Is there any fullrange driver that can keep up with the woofer section an be used in a large room?

Thanks