They are both nice cables. I have owned both interconnects, and the Quattro has a more balanced sound IMO (some would say neutral), with slightly more bass than the SPM. The SPM is slighty tilted towards the highs. I have also owned Red Dawn and Blue Heaven. As you go up the Nordost line, there is improvement. The Red Dawn I found to be slightly dry in comparison. Not dry in a bad way, just in comparison.
If you have trouble finding the Quattro in RCA used and you want two pairs, then look for a used 2 meter pair. I have heard that Nordost will cut them down and re-terminate them to new quality, for $100 per end ($400 total for 2 pairs, since 4 ends are already terminated). I do not know how they compare to those bought new, but since Nordost is doing the work, I assume good.
