Interconnect priority

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.

Thanks everyone.  I have Shunyata sigma v2 XLR between DAC>Pre & AQ WEL between Pre>Amp.  Though great before, the Sound is remarkably better than when I had Cardas clear light between DAC & Pre .

DAC to preamp!!!

From my experience…it highly depends. Each interconnect has its own priorities. For example with Acoustic Zen Silver Ref II and Matrix Ref II, the more expensive Silver Ref II always worked best between source and preamp with Matrix Ref Ii feeding the amplifier. The Silver is a more expensive cable but I will not say it’s a better cable, it’s different. It’s thinner and brighter sounding than the Matrix with more sparkle up top and thickening it up and taming that brightness with the Matrix from preamp to amp works best. Not so with the Absolute copper that’s very natural, smooth and open sounding. You want that cable between preamp and amp as all you’re going to accomplish if you use it on source is make the Matrix a bottleneck. So when we’re talking about a better cable, a bit more context wouldn’t hurt. Similar design but higher line from the same manufacturer, I would always put a better cable from pre to amp. 
Same goes for power cords. Best power cables make the most improvement on the amplifier(s). Ultimately you have to try and hear it for yourself - it’s very component and cable dependent.