Hi,
TI-RTOS doesn't support 6678 yet, use SYSBIOS instead: http://www.ti.com/tool/sysbios
Another way of getting SYSBIOS is installing the MCSDK: http://www.ti.com/tool/bioslinuxmcsdk
When you install the MCSDK you also get a version of SYSBIOS (and its examples), two demos (image processing and hua) that work with C6678 and some other packages that you'll certainly need while developing multicore applications.
J