I swapped I upgraded two of my WiFi routers to the Asus 3000 series....found the same issue with slow transmit when configured as a media server my exist Asus router. However; when I hooked the same router in a similar method - "poof" it worked. Pain in the back side until I figured out how Asus software was causing me more issues than I liked. And having more than one Asus router on the same subnet caused other issues.
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Going to have fun and play with hardware a bit...something tells me it will be as much fun or less than getting that wifi access point running.