Mapman, I have heard the HFC top ics and speaker wires on five systems now and never quite heard what I have on my two systems but nevertheless always heard a great improvement.
In answer to your question about less expensive ics that work as well, all I really know is that they are clearly better than my Exemplar Portal LLC balanced ics, which in turn were better than everything else I have ever heard.
I hate to think of all the trial and error involved in really answering your question about synergy. I do think there is some truth to it, but not enough to wipe out the total effect. I had the Exemplars for a long time on three different speakers, four different amps, seven preamps, two phono cables, and in two different rooms, I never heard any others that ever equaled or surpassed the Exemplars. The Skogrand SC Air Reference speaker cables, however, got very close.
Of cours, these experiences are not the total population of trials but they are enough for me.