Here's the kicker that will really get you - It "supports" 18Gbps, meaning it takes 18G in, compresses/throws about half of it away, then adds filler data at the back end to inflate it back up to 18! Damn marketing terms!

You are fully correct in that the transmission line cannot handle 18Gbps of data.

If you want an uncompressed extension solution, check out Inneos's Optical adapters.