At that price point, the Krell is not likely fully balanced, which means that the balanced connections actually involve more circuitry. As such, it's understandable that it doesn't sound as good.
Balanced vs unbalanced interconnects
I have a Wadia 830 feeding a Krell KAV-300i. This setup allows for the use of balanced and unbalanced connections simultaneously. I figured when I bought the Wadia I could finally run a balanced system. The dilemma is the single-ended connection always seems to sound better. The single-ended cable is a well worn SR Alpha Sterling. The balanced cables have been the SR Phase 2 Luminescence, Phase 2 Looking Glass, Alpha-core Micro Purl, and most recently a Kimber KCAG. Part of me says why fight it but… I have begun to wonder if the Krell is truly balanced throughout. Any ideas or suggestions out there? All cables are 1 meter in length.