icepower 500a input imp., a doubt...

[packman]

Hi guys, i have a commercial implementation that use 2 icepower
500a mkII with a traditional power supply (don't name it to dont hurt planner's sensibility), i hear great sound out of the amp (i use to drive a couple of B&W 801 matrix II speakers), very low distortion, great bass & mids but there is a noticeable rolloff of the high frequencies, i play drums so know well how real cymbals have to sound.
Reading the data sheet of the icepower 500a modules :

"The audio bandwidth is 60 kHz and the input impedance is approximately 8KOhm over the audio bandwidth. This presents an acceptable load for most pre-amps, active crossover outputs etc."

As a pre i use an acoustic reality pre-two (don't know output impedance unfortunately), with other end amp i don't hear that rolloff effect (but don't have the power and stage produced by the icepower), can be that LOW input impedance the problem?
If i want to try a passive preamp instead what you suggest to DIY/buy?
Thanks in advance

[peranders]

8 kohms in is not very low but it all depends how your pre amp look like.

What do you mean by roll off effect? Lack of treble?

[packman]

yes peranders, there are highs but lacks the extreme highs, like there is a soft rolloff over around 10KHz