Well, this was easier than I thought. I got my Raspberry Pi to boot and connected to it first with SSH and then with VNC Viewer. I installed the Octo drivers per the instructions on this forum, then downloaded Jack audio connection software and finally the unofficial version of Reaper for Linux with Arm processing.
Fired up Reaper, set the audio device to Jack, 6 in, 8 out and created 4 stereo busses in Reaper, each sending to a different pair of outputs.
I added a stereo track, set sends to all 4 busses from it and engaged the record button. I got audio on the input and on all 4 outputs.
I listened to all 8 outputs to verify that they work, changed the inputs in Reaper to the remaining 2 pairs to verify that they all work, and they sure are all working fine.
Next I inserted Parametric EQ and delay on every output bus, set the EQ's to 6 or 7 bands plus High Pass and Low Pass filters, and watched it all function smoothly on the first try. Here is a picture of my VNC session:
https://drive.google.com/file/d/0B_TU1z ... sp=sharing
As you can see the CPU utilization is in the 25% range. I can most likely load a FIR filter on the input for room correction with no real penalty on CPU.
Tomorrow I'm going to try and figure out the GPIO so that I have a volume control on a 10k pot and a mute on a push switch.