Hi Sean, good thing you brought up the cd output. It would have slipped my mind.
My initial setup was pretty satisfying. With my poweramp set to a notch before hitting mid level (visually balanced) for both channels' volume knobs, I had to turn down the CD player from volume 20 to around 3 or 6 (with remote) for soft recordings. That's the pain... my wife would accidentally move the power amp's left and right volume knobs and set it high that even with CD at lowest volume, it would be screaming loud. Happened once... and boy was I scared... so worried about the tweeters as I rushed to complete my evening shower (she cant hear "my screams" from the bathroom)! If it wasnt the main door being opened as always, I would have dashed out naked with bubbles all over just to turn down the left channel... : P
Anyway, after adding the Audiolab 8000C, the power amp is now set at max on both channels... for a more "balanced" loudness but volume knob of the preamp only needs a tiny turn clockwise from minimum (probably 1/12 of the max turn) for a decently loud playback. I find it pretty dangerous, frankly as, if she does the same mistake again on the preamp, boy history would repeat, this time even worse. So, yes, I think the signal from the Marantz 4000 is high enough for the 80 Watt/Ch amp. And a passive should work pretty well in that sense.