As much as I sing the praises of the QKore I do not like it with the RCA wire cable so far.
I only have a secondary SPDIF RCA input on the DAC, and another SPDIF RCA output on the Oppo player. On either I find the QKore to do little or even be a slight negative. But this is no doubt a limitation of devices available to connect it to. I have no pre-amp or integrated amp, so no unused analog RCA sockets to try it on. So the RCA cable just sits in the box for now.
Nordost has QKore USB cables, ethernet cables, XLR e.t.c So far I have not splurged the cash on trying any of these. If any of you did let us know what these connections did for you.