Bobo, When a change to a "better" power cord is made on a DAC or preamp there can be an improvement in apparent bass extension, and slam. You are correct that this performance has to be within the capability of the source component design, and presumes audition somewhere else has already demonstrated what the downstream amp and speakers are themselves capable of delivering.
When I began to use the top of the line power strip from Mapleshade for all my source components, there was improvement in bass extension, and slam! This was easily heard by non-audiophile family members, as well as by those who are supposed to hear the difference. Even a bigger improvement was noted when the same basic design in a power cord connected the amp directly into its own unmodified AC wall outlet. As Mae West was known to remark, you never know all of your capability, or something suggestive implying the same idea.
Someone just put up for sale an Aronov LS-9000 preamp, and I notice the ad mentioned the bass performance. No, not a relative of mine, although a set of reliable Audiogon ears.
