DTAs are relatively new technology, so I don't think the folks here have enough experience with them to answer your questions definitively. However, there have been lots of people reporting DTA failures, so it does seem like they're not well designed.
I had this same problem. Realized that my splitters have text on them showing that they drop the signal strength by 3 or 7 DB but noticed the signal in from the cable was 15db. Bought a $50 quad signal amplifier from Radio Shack and removed the splitters and used it and haven't had problems since.