Honestly, I don't know anything better than the new 18NS, but the Koda is one of the preamps that has caught my eye/ears, and I'd take a serious look at it. I don't know its current pricing, though, or even if it's available in your market.
As a darTZeel dealer (as if that was a bad thing to be...), and a long time customer, I think I know what works and what doesn't with it. Since you seem to want to keep your lovely 108, the 18NS is a great match. I've also tried the Constellation and Soulution preamps, the latter one also with built-in phonostage, and they were both splendid with the 108, worked beautifully, but I did end up preferring the 18NS for the added flexibility of the Zeel 50 ohm connection, that allowed me to move most of my setup to the side of the room, leaving only the amp (108) in between the speakers.