First of all don't try to communicate with riak itself (port 8089). All communications must be thru Riak-CS (port 8080)!
Then try to success using s3cmd:
Give us content of your .s3cfg
file?
In your case the minimum config is:
[default]
access_key = KEY
secret_key = SECRET
host_base = <root_host from riak-cs.conf>
host_bucket = %(bucket)s.<root_host from riak-cs.conf>
proxy_host = <ip of any cluster node>
proxy_port = 8080
Please be sure you use proxy_host -it should not be blank and should be ip address of one of Riak-CS cluster nodes. Otherwise s3cmd will try to resolve hostneme from host_base
and connect to it using http via tcp port 80 which is probably not what you want.
After you succeed with s3cmd you can go farther and show us Dragon Disk Account configuration, I'll tell you what's wrong with it.