Interconnect priority

DAC to preamp made the most significant difference in my system. What is lost at the source can't be gained further down the line. 

When I used Transparent Audio cables a few years ago, their hierarchy was source to pre most important, then speaker cables, then pre to amp...

Agree with all the above — closer to the source is more important.

Closest to source usually means lowest signal level. That's what matters in analog. 

Yes, most likely what folks say above. But it is dependent on the exact components. The good thing is they are most likely the same interconnects, so you can switch them and verify on your system. Unless of course, you have your components out of the way and amp in between your speakers (probably usually the best way)… then your preamp - amp is a really long connection.

If your equipment is between your speakers, consider moving it before you invest in the preamp - amp interconnect.