I need a few good suggestions: what is the best dual opamp to use to get a stereo microphone level signal amplified up to rca line level?

 

Are you sure the mic is stereo? That seems kind of unusual, stereo mics are quite rare and mostly used with proper matched mic preamp, not with just a dual opamp. Or are you trying to get some lo-fi sound?

I suggest you search for Green Pre, which is a bit more complex than one opamp per channel, but should have much better signal to noise ratio and less distortion than something extremely simple.

So anyway, what is the mic for and where does the signal go after amplification?

 

No, this is NOT a real microphone, but a 4-channel Radio Shack microphone mixer which unfortunately does not have line level outputs. It only has L/R (left&right) mic OUT. I need to get the signal back up to line level after it leaves this mixer. I used to use a tape deck with L/R mic inputs stuck in record mode for this purpose, but for a long time I've been wanting to build a dedicated device.

 

This site has some preamp circuits - http://www.discovercircuits.com/A/au-preamps.htm.

 

A preamp is simple. A low noise opamp with two resistors to set its gain.
A RadioCrap mixer is awful. Why not use a real mixer?