Akamai is just a CDN AFAIK, many online services do distribution through those guys. The choppy D/L speeds in duels is also normal, there is very little data used during the games, 99% of the loading times are the client setting the game up for a duel.
Perhaps set up a second NOX install with the multi-instance tool, D/L the game again and look in the Performance Monitor in task manager. This will tell you the IP of the Akamai server it’s using and work out where it is using IP lookup tools. Maybe it’s on the wrong side of the country or something? Changing DNS to OpenDNS or Google’s 184.108.40.206/220.127.116.11 DNS could maybe pick a server closer and you could see if it’s a geographical issue.
Also try a few tracerts to the Akamai server and see if there are hops consistently causing issues. With a game downloading a lot of little pieces a bad ping could maybe cause issues.