Least noisy pre-amplifier design
Look carefully at the specs for a digital pot, since they often are quite different than what you expect.  For example, look closely at these issues:


Noise:  Digital Potentiometers (DPs) often have terrible noise performance.  Rarely better than -80 dB THD+N, and often only -60dB or worse.  Many pots don't even put noise figures in the datasheets.  DPs are often only suitable for the worst quality consumer audio gear, or applications where noise isn't much of an issue (like LCD contrast adjustments).
Accuracy:  Many DPs only have a 20-30% accuracy on the total resistance from chip to chip (and sometimes between two pots on a single chip).  The MAX5460 has a nominal resistance of 100K, but can vary between 75K and 125K.  If you need two DPs to match, then you are out of luck.
Minimum resistance:  DPs often do not go down to 0 ohms.  Some only go down to 1K, or higher.  This can be super important if you are using the DP in the feedback path of an op-amp, to give you good gain control.  


I looked into using digital pots for gain control in audio applications and found them to be largely useless.  Instead I use relays (low noise, low resistance), Analog CMOS switches (good noise, small-ish), or even JFETs (cheapest, reasonable noise, hard to use).