Jake, although it certainly can be used as a marketing tool, it's far more than that. I've read enough about the tough series of tests that equipment has to go through to get THX certification(manufacturers discussing how thorough it is and how they had to make changes when problems were turned up)that I'm impressed. This of course doesn't guarantee that it's better than a similar piece of equipment without the certification, but it's a definite plus that it meets a set of standards.
As to the 1803 vs 6070, examine all the features carefully. Note that the 6070 has the interesting Circle Surround II processing, in addition to DPL II and DTS Neo:6. I was also impressed by the Sound & Vision test on the 6070. Whether the extra THX processing features added are audibly better is debatable and I don't have an opinion.
I suppose that I would lean toward the 6070. Note that their prices are nearly identical since both are available in the $400 area.
