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https://www.sparkfun.com/products/9118>
I'd need to read the rules carefully, but this looks like a good off-the-shelf solution that should be easy to work with for most teams -- provided this sort of thing is legal. It doesn't violate the safety-related reasons for being very careful with motor control and solves the "1 Encoder, 2 Jaguars" problem in a clean way.
I'd actually use one of these for each of the two Jags and power them both from the DSC, in fact you could send the encoder inputs to the DSC directly, and then to each Jag through one of the isolators (for a total of three places where the encoder data could be read, the DSC and the two Jags).