In this system, you would not need to purchase a SNAIC 4 whatsoever, cheap or otherwise. The Supercap requires one 5 PIN SNAIC from the Supernait’s pre-amp output. In this use, the Supercap is basically a high end Hi-Cap and the other potential uses are not available to the OP. The Naim interconnect which should have come supplied with your NAP 250 would then connect the Supercap’s output to the amp’s input. 4 PIN DIN > XLR stereo cable. The 4 PIN SNAIC would only be needed if you wanted to use the amp stage in the Supernait integrated.