Actually, this suggestion is brilliant. I have an old 442 mixer, 4 inputs with prefade direct outputs. This would open up at least channels 7-10. And it’s dc power, with a little fussing it could sit on my cart beneath the 664 (input knobs on the 442 are identical to the 664). I had thought about using it before, but hadn’t clicked on using the direct out to get to the iso, and then mix out to mix in on the 664. This would actually work for almost no money (a few cables) and let me focus on other important acquisitions. Also, I was thinking of incorporating some fixed microphones on our courtroom set. This would let me hardwire those into ch. 9-10, not impeding my 8 wireless channels. Wow. Thanks again for this idea. I’m glad I reached out for help.
I will also look at a 12 channel mixer. As you point out, not expensive option. And faders would be nice.