You can put the 3410 at the lower end of the first 50' coax if you insist, but that isn't the best location because signals will be 3 dB weaker before they are amplified. That might mean that the last TV will get signals that aren't as good as they could be.
Why can't you put the 3410 at the beginning of the first 50' coax just after the first splitter?
What does the adapter do?
As I said before, it's your system and you can put the 3410 any place you want, but I don't think it will work as well.
If you don't think my advice is good and you want to continue to change it, maybe you should just put a preamp like the CM7778 at the antenna instead of the 3410 and split as many times as you want using power passing splitters.
If I have given you bad advice, I'm sure that ADTech would shoot it down; he double checks my work.
