Wired is always better than wireless, if you can, do it !!! Wireless is only for convenience but as theorical 300mb/s for "N" and wired is 1000mb/s max (wired can actully it 900+mb/s while Wireless claims 300mb/s but it's at 100% signal, and 1 device on the network...)
For convenience as it's in stairs wireless is still good enough (highest ISP where i am is 200mb/s so 300mb/s on "N" is enough for now)
Yes i really love my Xonar, really worth it if you have a good speaker or headset (100$+) you'll notice an enormous difference and people that said onboard is good enough obviously never had a dedicated sound card
That said if you have a 20$ headset or cheap speakers, you'll probaly never see the difference...