The only thing I could suggest beyond that is a crossover similar to the Model 19 with separate mid/high adjustments. It would raise the xover to 1200 Hz but that should not cause an issue.
I agree, a mid adjustment would be sweet, but the stock XO is really a pretty good one albeit a PITA to work on as it's pretty stuffed.

His stock XO's should cross at 1500hz, they even have a bit of EQ built in to help smooth and perceivably extend the HF a bit with those 806's.