What's My Problem?

OK, here's the situation . . . . hoping some of you with more knowledge and experience than I have can help me out.

On 2-channel listening, my system sounds great at low levels -- say at 9 o'clock or less on my VPC-1 passive preamp volume. Lots of openness and air, good imaging, lots of space around instruments. Of course, dynamics and bass suffer, but that's to be expected.

Between 9 and 12, the sound starts to get harsher and the soundstage begins to close up -- orchestral stuff sounds much more confused and congested. Above 12 o'clock, it's really not worth listening to.

These aren't very high levels -- 9 o'clock is my "late night with the wife sleeping down the hall" listening level, and 12 o'clock doesn't get Verdi's "Requiem" to real-life SPLs.

My first assumption is that my amplifier just doesn't have enough juice. But the RB981 puts about 200 wpc into a 4 ohm load, and I would think that would be enough to get to at least decent levels, even with my admittedly power-hungry NHT 2.3As . . . .

Alternately, I thought that maybe the 9000ES/RB981 combo wasn't ideally suited for a passive preamp. I understand that component matching is critical here, but I'm not really clear on how it works . . . . the volume gets loud enough with no problem, it's just that the quality suffers.

Then again, it could simply be "louder=more annoyance from digital harshness," and I need to replace the 9000ES with a better Redbook CDP. But it seems to me that if the CDP was to blame, the soundstage and "airy-ness" wouldn't change much as the volume increased.

Suggestions would be greatly appreciated!

Thanks!

Pat