Best power cord to use with a Krell preamp.

I'm using Krell equipment with a pair of B&W N 802s, and using Synergistic Research cables throughout. However I'm dissatisfied with my power cord selection, which is thier AC Master Coupler. I've also tried thier Reference AC Master Coupler. Although it seams to open the sound stage I loose inner details and well as dynamics. Any suggestions?