Understanding Plot Showing Impedance, Resistance, and Reactance
It looks like the impedance is about 1K-2K through your band of interest.  I don't know what you mean by "much more," but 20K input impedance for your preamp should probably be easily achievable, and 200K wouldn't be much of a challenge.  Note that your internal resistance is significantly lower--almost negligible--but the impedance will still affect both the output level and (perhaps more significantly) the phase shift.  If phase shift is critical (which I doubt, but you're the expert on your requirements) it could be compensated for in the preamp.