Speaker cable advice

I also have a REGA ISIS Valve cdp/DAC. REGA OSIRIS integrated amp and new HARBETH 30.2 XD’s.

With the new HARBETHs, my upgrade path that worked for me just as you asked (warmer, more presence …) was to upgrade from an all NORDOST FREY cables loom to CARDAS CLEAR XLR ICs first.

The CARDAS CLEAR Speaker cables were the next to follow in good form but the largest impact was from the ICs.

The last piece in progress will be CARDAS CLEAR BEYOND power cables (demoed but not bought yet)

FWIW.

Aftermarket cables for headphones is an easy way to test silver vs copper cables. I've done it before and there is a difference.

The difference is slight, but it exists. If you wish to test it on your system..ask a dealer to loan you a cable to try out/swap between what you're already using.

The sound signature of a cable depends on more than just its conductor. 

Aftermarket cables for headphones is an easy way to test silver vs copper cables. I've done it before and there is a difference.

I think you’re a bit out of your depth here.  Silver cables can sound like copper and vice versa — all depends on the overall implementation.  Hearing a difference between a couple headphone cables is not proof of anything.  In any event, overgeneralizing and telling someone to just avoid silver cables is misleading and could cause the OP to ignore some outstanding options, which would be a shame. 

Previous cables were all Clear Days, with the Double Shotgun and Paul’s jumpers. Very nice cables and I enjoyed them for many years. Still loved the faces on the sales staff at a local shop when I took them in and we compared them to Kimber 4TC which is probably a similar priced cable. They were astonished to hear how more open and natural Paul’s cables were and sad when I told them the price and he only sold direct. A couple of them ended up buying cables from Paul for their own systems and recommended them to clients. Paul was a great guy. 

I later sold them off and landed with WyWires after talking with Dan Wright. The WyWires are more open, sound less closed in and made my speakers disappear, where as good as the Clear Days were, I struggled with them on that task. Not sure the WyWires really warmed things up, but I did feel the Clear Days were a tad cooler, and maybe a little thin in comparison.
You didn’t mention you interconnects, which would be helpful to know.