active or passive?

You can use a passive preamp when you have a buffer like an active cross-over IMHO. Otherwise you loose dynamics.

Passive preamp in most cases will not suffice for KSA.

Marakanetz, interesting answer, mine works great with my ksa-250. The ksa-150 is even better match. What did you base your answer on?

low sencitivity 1.7V for full output power requires the line source to have an adequate or higher which is not often the case...

Most cdp (not all) will have no trouble with that, I have a sony player (xa777) and the krell ksa-250 is 2.2V for full output. I do have transformer PVC which may or may not help out with mine. I have read that the F.T. audio passive also works fine with the krell's with most cdp's. of 2V output. When I spoke to Guy at placette audio he also said his would work fine in my setup (did not try it).