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.
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.