A tube-based stereo microphone preamp might be a good idea...  

There's a lot of entries, though... And from people who've been doing this a long time... Nowadays, mic pre's are used mostly for color and tonality rather that just gain stages... Especially the tube models, which boast various type of transformers that add some kind of wanted effect to an individual singer or instrumentalist...

Also, I think the stated need for them is somewhat hyped... Especially in computer-based recording, where so many plug-in effects can be utilized very cheaply instead of buying relatively expensive hardware...

Some mics, like ribbons need a microphone preamplifier to bring the gain up to useable level... Although there are now active ribbons that don't need a preamp...

Anyway, good idea...   (m.)