I would definitely go direct. Adding whatever your preamp or other component is in the middle will just add more amplification stages and reduce the purity of the signal. In my case, I tried running the KSE1500 from the headphone out (or perhaps the rear RCA outs?) of my PS Audio BHK, a reasonably high-end tubed preamp. But it added audible noise. I got much better results running RCA directly from the outputs of my DAC (also PS Audio). It sounds like you need an RCA stereo (your source) to 3.5mm cable (KSE input). I have one from ADL which is fine, and a very nice Moon Audio Silver Dragon v3 for more money. But removing intermediate gear is going to make a lot more difference than the cable. Use the best source you can, and connect to it directly.