That sound card can drive 7.1 analogue speaker set. It's optical output is a bit confusing with mention of pairing it with side channels so does that mean optical outputs 5.1 compressed dolby and additional 2 side channels from analogue connectors to make 7.1?, not sure.
Summary
No problems running 7.1 analogue speakers, true 7.1 as each speaker has it's own channel. Each 3.5mm jack accommodates 2 channels each.
Not sure about optical. Optical is usually limited to 2.1 pcm uncompressed audio, so not sure if Asus has payed for dolby/dts licencing to encode in real-time, so setting 5.1 or 7.1 might not be possible.
As for headphones with 7.1 drivers, it is kind of true surround but because each driver is in close proximity to ear...