The ADC they use has an input impedance of greater than 10 GΩ, so I do not expect filter loading, although I would assume an active filter would entirely eliminate any concerns.
Yes, I suppose I did not explain this very well. The first order filter uses a nominally 0.1uF capacitor and a 3.3kΩ resistor. The second order filters used the same 0.1uF capacitors, but with a 2kΩ resistors. For the decade separation filter, the same 2kΩ resistor was used, but the second stages used a 20kΩ resistor with a 0.01uF capacitor. The models used the measured values for resistance and capacitance.
Now that you mention it, there is probably a nice IC containing higher order filters, right? Looks like Maxim makes a few. Can anyone recommend any IC's to accomplish this? I'm fine with passive resistors, but if there's a nice filter out there that already exists, why reinvent the wheel.