recording question (mic vs. line)

[rif <rif@xxxxxxx>]

I'm doing some speech recognition work, but my background is not in
audio per se, and I'm running into some difficulties.

I'm interested in recording speech simultaneously through two mics
(one near- and one far-field), so that I can have paired recordings.
My computer soundcard has a mic in, which is mono, and a line in,
which is stereo.  My basic plan is to feed both microphones into a
mixer (Behringer MX602A), put out a stereo line-level signal to my
computer, record that, and separate the channels later using sox (this
is all in linux).  While this technique works, I find that no matter
how I seem to adjust the gains (in either the mixer or the soundcard),
the quality I get from the far-field mic is much lower than if I
simply plug the far-field mic directly into the mic in on the
soundcard and record that.

Is what I'm trying to do fundamentally reasonable, or am I always
going to lose a lot of quality boosting a computer mic to line level?
Maybe I need a soundcard with multiple mic inputs, and some relevant
software? I said, my goal is to record from two mics simultaneously in
a way that lets me obtain separate recordings of the same signal, but
I don't want to lose a lot of quality with my setup.  Any suggestions
or advice are most appreciated.

Cheers,

rif