I have been using the Signal Cable Silver Resolutions since 2008 in bi-wire config. I have been very happy with Signal Cables. Used Nordost 4-flat bi-wires previously. The upgrade was significant. And yes, bi-wiring made a big difference for me, even when I was using the Nordost 4-flats.
I do not have experience with tubes and cannot comment on that.
I do not have experience with tubes and cannot comment on that.