This is the latest RE SS spreader bar I just run a single 5mm dyneema rope that I've spliced a 3mm dyneema rope inside. This rope has had just over 100 hrs approx actual water time and its only showing really minimal wear because I use a pulley. Antal rings next best for stopping rope wear, but a single stainless ring is the worst closely followed by direct connecting the chicken loop rope. Anything that forces the rope to slide across a very small diameter ring or stainless chicken loop replacement a few brands offer will wear the rope quite quickly.
Pulleys and antal rings were designed to slide on rope with minimal damage to the rope.
The pulley is this one
www.kitepower.com.au/products/30mm-ronstan-pulley-w-swivel-shakle-head?variant=4981422915623The pulleys is more than strong enough. The rope with 3mm inside 5mm would have a breaking load of at least around 3000kg, so there is no need to worry about rigging compression loads/angles.
Just inspect your rope regularly, no need to worry about a secondary rope when using antal rings or pulleys set up like this, and like Pearl said you can still ride back to shore after relaunching if it did break.
If you use a SS ring or direct connect the chicken loop with a SS talon or duotone rope harness kite maybe its best to run 2 ropes? Running a Plastic chicken loop directly on the rope will wear out the chicken loop and they can be quite expensive to replace.