Thanks Marko.
My giant killer is a cable -- the Sound Quest Pro Series Zero Point Reference XLR Interconnect. Fantastic neutrality and transparency (I think those are different) for next to nothing. I finally replaced them with very expensive reference cables (it took me a long while to find something better than the Sound Quests) and then changed systems which allowed me to use very inexpensive BNC 75 ohm connectors between the preamp and amps. So, I sold the reference cables but still have those Sound Quests.
As a more pricey "giant killer", the Perpetual Tech DACs (1a and 3a, the latter Wright modified, powered by a Wright power supply) are wonderful for the money. I tried other more expensive DACs and simply couldn't justify the move to a pricier system. That says a lot because, unfortunately, I'm not afraid to spend money for sonic improvements ;-) Different DAC's did present a different sound but something important always sounded worse than the Perp Techs to me. Of course, I have not yet heard some of the Giant Killer DAC's mentioned earlier in this thread. They might be "Giant Killer" killers!