Came across this thread and it was a bit of a head scratcher too...
The TX-SR600 is a good many years old now (I still own mine from my first surround system) so I assume the OP is looking used?
Still -- the 600 NEVER gave me any issues, and had survived a cross country move after sitting in 120+ degree heat in a garage for well over a year, and it's STILL going in a gym system. I don't know what the second poster was talking about with regard to "drowned out levels," but this never occurred with my 600. I would recommend it if you're looking used and don't need decoding for the Blu-ray lossless formats (the 600 will do Dolby Digital EX and DTS ES and offers six amp channels).