DIY simple crossover for pedalboard

[Guitarist]

I'm thinking of add a couple small speakers to the L/R of my pedal board. The board may be the baffle and have them mounted open back.
I've got a few smaller tube amps and now a tiny 12V TA2020 amp which only likes 4Ω though. Often I'll run all my pedals on a 12 V. lithium battery. A sub (have one here) will handle all the lows and sit behind.

The signal is buffered by this stage so 1) basic idea is to just isolate the two tones by Y'ing with two 220K resistors perhaps (vs. j201s) then adding caps? Any ideas here.

Besides rackmount there seem to be few smaller sized crossovers.

I never seem to have enough bass even with stereo 4x12s with one Eminence bass speakers in the far/bottom corners Getting lazy too...)

EDIT: Maybe this would work too: http://www.amazon.com/Clarion-EQS746...pr_product_top

[Steve Conner]

I once built a crossover to add a sub to my home studio monitoring system. I made some 2nd order active filters using the recipe from The Art Of Electronics. IIRC, a 100Hz high pass filter for the main speakers with a Linkwitz-Riley Q. The sub already had a lowpass built in, I just had to make a mono sum output for it.

I could never get it to sound right, so I gave up on it. But recently I installed the same sub and crossover in a friend's system and it sounded great at any setting of the sub controls. I blame bad room acoustics.