[sdiy] Mixer Design Question

[alfred.pear at gmail.com]

Hi -

I'm relatively new to electronics building and op amps have been
keeping me suitably occupied.
However, I have a particular application and I can't quite wrap my
head around the circuit design and was hoping someone would be kind
enough to help me.

Essentially, I'd like six independent channels to use as discrete
pre-amps, but I would also like the option of patching them into a
single, final stage with an overall gain control.

Is there a design where I can maintain the integrity of the singular
pre-amps, while having an overall final mix in a separate output?

Since I'm not totally at home with diodes yet, if they are necessary,
is there a way to do this while maintaining both polarities in the
final stage?

Thanks to all,
Al