You won't go wrong with Behringer, Mackie, Edirol or Tapco audio mixers.
I suggest this Behringer Xenyx for an excellent low-cost option: http://www.amazon.com/gp/product/B00...SIN=B000J5XS3C
It's only $65 shipped!
By far one of the cheaper items for your video hardware restoration suite.
Note that while audio mixers go up in cost, they mostly begin to offer effects and features that are important to musicians only -- not videographers. We can get by quite well with basic mixer gear, to provide some degree of external hardware control to the audio, such as gain and basic EQ.
Here's some previous threads on the subject:
And then you can either skip software corrections, or simply have better source to start with for the software phase of restoration, filtering and improving your audio.