You have some other options to consider beyond just replacing the pots with digipots. That's initially appealing because it sounds so simple, but in practice it may not be the best solution. Other possibilities are:
1) DAC controlling VCA gain - either linear OTA like LM13700 or exponential VCA like V2164 or THAT 2181. There are now CEM chip clones available too - AS3360 and AS3330.
2) Multiplying DAC controlling levels or gains (MDAC). This is great option, since it's basically a one-chip solution. You can fairly easily find 10 or 12-bit MDACs, which you won't mange with digital pots. Bonus points if you've got an easy solution for bipolar Vref inputs (some MDACs duo this, but by no means all).
3) Replace non-signal path parts with digital elements. Instead of controlling an LFO's rate and depth with digipots (for example), you can generate the LFO digitally and output it at the required rate and depth. Since you're dealing with LFO frequencies, the sample rate demands are low and you can easily provide vastly excessive (in theory terms) sample rates and use simple filters to provide an indistinguishable-from-analog output.
I think there are others but it's getting late and I can't recall them right now. Anyone else care to step in?
Tom