Bi-amp Audio Research and Bryston 4B

I have a question with the above subject concerning bi-amping with a 
Sonic Frontiers Line One tube preamp. Both amps will be accompanying 
Martin Logan Sequel 2 speakers, all at 8 ohms. I will use the Bryston
for the woofers and the A.R.C. for the panels. The D115 has level
controls, but I am unsure if it will be adjustable enough to blend
equal output for both amps sonically. The Bryston is hooked up with a
balanced output from the preamp and the D 115 is single ended. I
realize if I have too much base that I can use single ended to my B4
to lower by 6db. and maybe equalize better on the base/panel Martin
Logans. Barring purchasing an outboard adjustable crossover (Bryston's
is around  $1300.00) - any other suggestions from the group here
please?

Regards,
Tony.