Which IC is more important?

The source to pre IC carries a lower voltage signal so, the less the sonic interference of the conductor, the more "true to source" is the sound going to the pre. This said, different cables perform *differently* at different placements in the system (lots of differents here, sorry). Trial is the way to go -- another trick is to use the same cables throughout if you like the sonic signature (or lack thereof). The logical sequence would be, source->pre, pre->power.

BUT, cables performance in some systems is a function of system x voltage...

I, for one, would expect that Sugar's siltech/quattro combo is best as is, rather than the other way round: in my experience, the quattros were better with higher voltages. Sugar knows best, but maybe he doesn't need to afford a 2nd quattro.

I used the low to higher voltage sequence when assessing cable upgrades.
Cheers!

One sentence - what is lost at the beginning cannot be recovered...

RGD you are briliant.You could not in fewer words some up the biggest audio truth that exists.
That is also why the SOURCE IS YOUR MOST IMPORTANT PART OF YOUR SYSTEM.Not the speakers.Bravo

Which ever one sounds the best where ever it is located is the most important.