Problems after installing SSD as second drive.

I've installed a Samsung 840 SSD to the second SATA-Port of my iMac along this tutorial: Installing iMac Intel 21.5" EMC 2428 Dual Hard Drive Kit. HDD is still on first SATA-Port, OpticalDrive is still on thirst SATA-Port. Then i've installed Mountain Lion on SSD and made it bootable. SSD and HDD work fine. But, after this modification i have problems with all USB-Devices, Firewire-Devices and the OpticalDrive. DataStreams break up constantly, so transfering data to external devices is very slow and jerky, also reading from DVD. Burning a DVD is really impossible because break of DataStream. Getting following error: Unable to burn. The disc drive didn't respond properly and can't recover or retry. Sometimes I also loose connection to USB-Devices. Everything worked fine with Lion and without SSD.

My first idea was, that the SSD slows down the USB-Controller but i have no idea why the OpticalDrive and Firewire are affected too. Maybe then the problem is the Bus between controllers and CPU/Ram? Does anybody know something about this problem?