The aim of the DoS attack is simply to stop you using Sythe.org. That's what a DoS attack is. Denial of service. Ie the attacker denies you the right to use this site by whatever means possible.
When the site gets attacked I have to login and filter the traffic manually. There are something like 20,000 blocked IPs in the firewall from probably a couple dozen seperate botnets. I have nfi why, but sythe.org is a huge target for botnet attack.
The good thing is that once a botnet is blocked it basically can't hurt the site anymore. But unfortunately most of that blocking has to be done by hand.