this is difference case, you can read my post carefully and will understand
summary:
1. if don't use the multiminer, vga 797 will load 99% and get over 700K with Intensity=13
2. if using the multiminer, vga 797 only load 96% and get under 600K with Intensity=13
multiminer only work good with Inversity over 13
You use the EXACT same parameters as you do in your multiminer, right? mine hashes at 638 when i run on CGminer, multiminer reports 640, about correct.