Martin Colloms, reviewing Wadia 860 or 861 for Stereophile, said guardedly that he thought a very good active preamp was necessary for best performance. From my own experience with an Accuphase DP-75 and a CAT SLT Mk III with factory simplified signal path, I disagree--unless the active preamp is simply offering a partial filtering out of some nasties built into the Wadia, which I hasten to say I've never heard. Ask yourself: how could an active preamp help? It isn't the same issue as active versus passive preamp when the CD player must be plugged into one or the other, putting a third element into the impedance equation. (Maybe some wise person among us can answer my question, which I posed as a rhetorical one--but maybe it's not.)
