I was using the -d flag, but it wasn't enough. I was able to get two cgminer instances running by using the "--remove-disabled" option (as found here:
https://bitcointalk.org/index.php?topic=227230.0). It tells the cgminer instance to completely ignore the other GPUs on the system.
Script 1:
export DISPLAY=:0
export GPU_USE_SYNC_OBJECTS=1
export GPU_MAX_ALLOC_PERCENT=100
./cgminer -o tcp+stratum://pooledbits.com:8338 -u <user> -p x --scrypt --api-listen --api-network -I 18 --auto-fan --gpu-powertune 20 --gpu-engine 960 --gpu-memclock 1220 --gpu-platform 0 -d 0 --remove-disabled -w 256 -v 1 -g 1 -l 1 --thread-concurrency 8000
Script 2:
export DISPLAY=:0
export GPU_USE_SYNC_OBJECTS=1
export GPU_MAX_ALLOC_PERCENT=100
./cgminer -o tcp+stratum://pooledbits.com:8338 -u <user> -p x --scrypt --api-listen --api-network -I 20 --auto-fan --gpu-powertune 20 --gpu-engine 900 --gpu-memclock 1250 --gpu-platform 0 -d 0 --remove-disabled -w 256 -v 1 -g 1 -l 1 --thread-concurrency 21712
However, I'm still having the HW errors on my 7770. It's using the options specified in Script 1, and it having lots of HW errors. After running for 10 minutes, I had almost 900 errors. My video card is an MSI R7770-PMD1G5d:
http://www.msi.com/product/vga/R7770-PMD1GD5.htmlIt's supposed to be able to run at 1 GHz and has "4500" MHz Memory (I don't actually believe that, so I set it to 1220).