Right, I realize that the power circuit I built already will need to be revised so that it can bring the little mics up to line level. The Delta 1010 linked above has exactly 6 RCA line inputs.. perfect! I'd found this earlier - http://www.epanorama.net/circuits/micamp.html
- not sure if the LM358 that you linked or the BJT amp will have better quality. We'll have to try both!
Mixer was my first thought as well but they are very expensive even for 2 inputs, and use XLR / 48V inputs which we don't want to deal with.. line in is way easier, and better transfers to DSP and microcontroller later.