I asked Dr. Bews the following question - are all your Interconnects / Speaker Cables solid core? If so what is the advantage in sound quality terms over normal copper multi -strand even of quite high quality? He replied as follows:
All Interconnects use multi-strand PC-OCC (Grainless copper or Monocrystal copper are other names) for copper Interconnects, since OFC sounds unpleasant in comparison (this also applies to some degree in speaker cable design).
The type of dielectric has to be chosen for the conductor geometry (Spirolink IV uses a dual dielectric of modified PVC/PTFE to achieve sound, whereas the Grainless interconnect uses polyethylene dielectric and the conductor is unusual multi-strand PC-OCC).
The silver cables uses multi-diameter silver i.e. different diameter of solid core wire to form conductor with PTFE or silicon rubber dielectric.
For Speaker Cables: Spiroflex is solid core design with PC-OCC copper and PTFE dielectric.
The Hybrid Ribbon uses a foil of LC-OFC type copper (Modified PVC dielectric) for one conductor and a multi-strand PC-OCC conductor (polypropylene dielectric) for other conductor.
The Grainless biwire uses a multi-strand PC-OCC conductor (polypropylene dielectric) for bass and solid core PC-OCC conductor (PTFE dielectric) for top end.
You need to mix the conductor sound (solid core or multi-strand, PC-OCC or LC-OFC grain structure) with the sound of the dielectric to get the balance to the sound you require. The connectors have some influence, so a good choice of connector is required as well.
Cable design is as much an art as a science.