MOTM

I apologize for the OT but any suggestion would be highly appreciated.
I had posted the same in the Oakley list days ago but got no reply.
I wanted to purchase a line mixer with very simple features but I
don't think there's anything available that matches my needs. What
I'm looking for should have about 20-24 balanced line inputs, no gain
no attenuators, only a panpot controller on each (mono!) channel and
a stereo output with master volume, that's all. I need it to connect
my two TX816 (8 balanced outputs each) and another two keyboards.
Item offered in the shops are mainly with stereo pair inputs and
balance control for the pair that has nothing to do with panpot on
each channel. Maybe somebody here in the list can suggest a simple
diy project that I could try to build, in the end even a more simple 
design, many mono inputs and only one mono output (with attenuator)
would be fine. I'm sure many people in this list can give precious 
tips, many thanks.
Enrico (Italy)