I think of transparency in regards to an audio preamp as the ability to bring mic level to line level without altering the sound.What you get on tape is pretty much what you hear as you record it.If a unit colors the sound that means to me it is adding something or changing the signal in some way.Some people prefer a "colored"preamp(although with cheap preamps warmth is often confused with mud,IMO).I like a preamp that adds next to nothing to the sound,of course that might be because I cant afford any QUALITY preamps that color the sound.As far as stereo miccing,you would run two signals from your mixer to two channels on your multitrack(or a stereo channel).