The bulk of the work the stereomour is going to do will be run the coax drivers. I want to say they are crossed over to the sub amp at 200hz. Will it be worth putting a high pass filter in the line to take the 200hz and below out of the mix even if the coax aren't going to run it? I know the bottlehead can take it, I just hear things about making the amp load even easier. Would it matter?
Is the sub amp taking the speaker level inputs, or will you wire a line level out from the Stereomour?
The Stereomour has two easy places to implement a high pass filter - in the 0.1uF coupling cap, and the parallel feed cap.
Paul Joppa generally recommends downsizing the parallel feed cap, and I think he prefers this because doing so can drop the physical size and cost of the cap (so you can use a nicer part) and it will kick out some of the 60Hz hum from the DHT filament. (I haven't asked PJ about this specifically, these are my assumptions).
I don't see why you couldn't also lower the value of the 0.1uF coupling cap (or lower the value of the 249K grid leak resistor) in accordance with shrinking the parallel feed capacitors for an even steeper rolloff (if you want it).
Still, I'd build it bone stock first, then mess around with these things.
-PB