"kernel" : "scrypt",
That option has never worked for me it starts but then tries to mine btc on a ltc pool when I use it I need the --scrypt when starting on the command line then it will actually mine ltc. Here is the file I use when starting it.
cat ltc.sh
export GPU_USE_SYNC_OBJECTS=1
export GPU_MAX_ALLOC_PERCENT=100
export DISPLAY=:0
cd ~
cp .cgminer/cgminer.conf-ltc .cgminer/cgminer.conf
~/cgminer-2.8.5 --scrypt --api-listen --api-allow W:127.0.0.1,R:192.168.0.0/24 -g 1
All other options are in the cgminer.conf. except the core/memory speeds I need to set it manually with another file as if in the .conf file they don't seem to take effect. For your 6950 I find that worksize 256 vectors 4 intensity18 and speeds of 800,1250 get me the best result of nearly 400kh/s on the one I have.
Edit: Here is the cgminer.conf I use as well for the 6950 the threads are 7040 that I use, it is the first card in this conf file.
cat .cgminer/cgminer.conf
{
"pools" : [
.......
],
"auto-fan" : true,
"auto-gpu" : true,
"temp-target" : "81",
"gpu-fan" : "0-100",
"intensity" : "18,13",
"vectors" : "4,4",
"worksize" : "256,256",
"thread-concurrency" : "7040,8192",
"log" : "5",
"queue" : "1",
"retry-pause" : "5",
"scan-time" : "60",
"donation" : "0",
"shares" : "0",
"kernel-path" : "/usr/local/bin"
}