Which Cables Are of Most Importance?

IC and Speaker are far more important than power and HDMI. The later two provide questionable benefit.

I have a Mcintosh/B&w system. In mine the ICs and speaker wire made a huge difference as I had cheap cables from my 90's system. I demoed a set of modest cables installing one at a time and could hear improvements each time which helped justify ordering a complete IC/speaker set. With the power cables I tried a cheap pair, heard a small improvement, so I did replaced all but is only a slight difference in my setup. I know nothing about HDMI but would try a cheaper upgrade and see what happens, if you notice any improvements try an even better one.

I feel that ALL cables are important - they can be as important in enabling your systems full potential, just as much as any component. Having said that, let me qualify that it will depend on how sensitive your equipment is – Mid-Fi gear won't showcase this.

Now, I would have agreed with 'Jaxwired' as of last year but my eyes (and ears) have been since fully opened, and to finally answer your question - always start with a solid foundation - excellent power cords and clean power.

All cable(s) are important. Your 1st replacement is the Power Cord.