Volume level mystery - can you solve it?

I recently replaced a pair of Linn LK power amps (85 and 140, in passive biamp mode) with the much more powerful Linn 2250 amp (just one). My preamp is a Linn Kairn. I have noticed that in order to achieve the same volume levels with the 2250 as I was getting with the 85/140 combo, I need to crank the Kairn volume setting much higher. By way of example: on a scale of 1-100, 50 used to be my normal listening level, but to achieve that level I now need to turn the Kairn up to 70 or higher. The Kairn only goes up to 100, but with the new amp, everything below 60 or so is very, very quiet. After 70, the volume ramps up pretty quickly, whereas with the 85/140, the distribution seemed more of an even straight line graph. Does anyone have any idea what this is all about? Are amps just calibrated differently? If anything, I would have expected the 2250 -- a more powerful amp -- to produce higher volume at lower settings, but the reverse seems to be true. Any thoughts about this would be much appreciated. I am a little worried that something is wrong with the amp, but aside from the volume issue the sound seems good. Thanks.
Here are some gain, impedance and other stats. For those who know about these things, perhaps they help answer the question. Gain looks approximately similar across the board, but input impedance looks different, although I can't interpret the information.

Please let me know what you think.

1. 2250 Amp (which I am using now and which requires me to jack up the volume dial on my preamp):

Unbalanced 28.3dB
Balanced 22.3dB [NOTE -- I use unbalanced]

Input Impedance
Unbalanced 7K8ohms
Balanced 7K8ohms

Input Level for Clipping
Unbalanced 1.2V rms
Balanced 2.4V rms

Output Power
230W rms into 4 ohms
115W rms into 8 ohms

Maximum Input Power

Typical Operating Input Power

2. LK 140

x27 (28.6dB)

Input impedance

Input signal for maximum output
870mV rms

Maximum input power

3. LK 85

x27 (28.6dB)

Input impedance

Input signal for maximum output
685mV rms

Maximum input power
I agree, it could be that running the two older amps in passive biamp may have had the effect of summing their input impedances, which is greater than the single new amp, and thus presenting a different load to the preamp.

To test this theory out just run one of your older amps full range and see what kind of gain issues you have then.
Gunbei, I no longer have my old amps, but wouldn't higher impedance require turning the volume up higher on the preamp?
Ahhh, too bad.

I'll throw out some hypothetical numbers here just for the sake of illustrating an example.

Say, one of you old amps had an input impedance of 47Kohms and the other old amp you were combining it with had an input impedance of 23Kohms. Your preamp would see them as 70Kohms. But if you reconfigured your set up so you were just using a single amp with 47Kohms or less, this new amp might require more gain to attain the same volume levels as your two older amps being used together.
One other possible solution to the mystery: from looking at the owner's manual I see that there is a small button on the back of the unit that switches from balanced to unbalanced. I have cabled the unit for unbalanced, but never checked to see what position the switch was in (because I doidn't notice it). I am not at home to check, but i wonder if this could explain the problem.