Alta Vista NP-100 input impedance?

I'm looking at a Primaluna pre amp to run my pair of Alta Vista NP-100 (UG'd Counterpoint SA-12s).  It appears that the PrimaLuna works best on high input  impendance (~28k Ohms?) power amps.  I have no idea what the impedance on my amps are or have the tools/knowledge to calculate such.  I do know the P-100s are the low sensitity ones (use 6SN7s instead another tube).  Pre-amp being replaced is a Counterpoint SA-7.1