Preamp output voltage...affect on volume???

That difference in output impedance isn't enough to make any difference. Until you find out what the gain of the Classe is we are wasting our time speculating about the difference.

Quite simply a higher gain will result in a louder sound. The volume dial alows you to adjust the gain. A higher maximum ouput implies nothing unless you know the maximum input level.

Suppose that all signals are RCA line level and unbalanced; input is designed for a max of roughly 2 Vrms and therefore the gain at maximum output appears to be at least 25.

Suppose that all signals are line level and balanced; input is designed for a max of roughly 4 Vrms and therefore the gain at maximum output appears to be at least 12.

These high gains are unusual for a hi-fi pre-amp as most pre-amps are close to unity gain at maximum levels...the advantage will be better immunity to RF/EM noise (likely a lower noise floor downstage of the preamp).

To get back to normal volume levels you need to;

1) reduce the power amplifier gain stages to compensate for a large signal at the input of the power amplifier
2) attenuate the signal so that it matches the input capabilities of the power amplifier.
3) get a power amplifier that is specifically designed to accept this higher range of input signals

Good power amplifiers will often have potentiometers to provide flexibilty to handle various input level ranges.

I got a response from BAT that explains the difference in volume control between my Classe preamp and the VK-52se even though they both have similar gain. I guess it comes down to digital volume control (Classe) vs discrete volume control (BAT). By the way, what is a "Discrete" volume control? Can someone explain why discrete volume control does not have as much attenuation as digital control?

Below is an exerpt from the email I got BAT sent me:

"...integrated digital volume controls give
you more room - they have 180 or more steps, allowing you to achieve greater
attenuation. I don't have solid information on Classe, but what you are
telling me is consistent with a use of such a volume control.

High quality discrete volume controls usually stop sooner. Reasons are
practical - cost and complexity...It is many times more expensive
than the integrated circuit attenuator. The reason we use that expensive
solution is the sound, of course.

Our volume attenuator has linear range of 70dB. We do not go further as
doing so would degrade the signal way too much. -60dB attenuation means you
are throwing away 99.9% of signal, letting just 1/1000 of it go through -
hardly good situation."

The maximun gain is within 3dB, not enough to explain the difference.

The output impedance is essentially the same compared to the input impedance of the amp.

The input impedance of each compared to the output impedance of the CDP should make no difference.

That leaves us with the taper of the volume controls. The only logical explanation I can see is that the louder one's steps are bigger at lower volumes than the other one. Have you contacted the manufacturers to see what they have to say?

If you want to ship them both to me I can measure the gain at the different control settings. You could do this yourself with a test CD and a cheap multimeter if you really want to know.