Furutech Evolution II Interconnects

I like the FP-108 best for rca because of the PCOCC center pin and because I personally like the solid center pin instead of their center pins that have a bunch of thin wires to make contact. The FP-108 facilitates a "crimp" type connection via a set screw. The FP-110 can also be considered (solid PCOCC center pin but in gold not rhodium like the FP-108) For some reason, the FP-110 must be soldered and does not have a crimp style set screw connection like the 108.
I have also made several pairs of XLR cables from this wire using the excellent FP-601/602 XLR connectors - these need to be soldered.

So, the FP-106 has a different center pin than the FP-108?

The 108 and 110 have OCC solid center pins treated with their alpha process.
The 106 has what they call their "filament" center pin (which is comprised of small spring tensioned wires) and those are phosphor bronze, probably because copper would not stand up to the repeated tensioning and release of connecting and unconnecting the rca plug. This is why pure copper is not usually used in electrical outlets, etc.
The 106 does have set screw connections (same as the 108 but not the 110), so no soldering, and it is a fine sounding connector. The 106R is used in their Reference line of finished cables while the 110G is used in the Evolution line. Interestingly, for their flagship Lineflux cables, they use the CF-102R rca plugs that have a solid center OCC rhodium plated conductor, like the 110 plugs used on the Evolution line.
All their plugs work and sound great, and you can choose between the typical sonic differences between rhodium and gold plating. I personally like the solid center pin over the filament pin, just personal preference.