I'm sure you are doing something wrong, what kind of algorithm is this coin you mining using? Is it a cryptonight algo coin or what? Anyways I have same card and it's only ETH that's the most profitable to mine with 6600XT, oh also make sure you activate compute mode in Radeon settings
The algo is CryptoNight_GPU. Like I stated earlier, I have a gigahash on ETH but since this coin wont be POW forever I'd like to compile some alt coin testing.