First let me

you to the group
next maybe a mod can break this off to its own thread

and i would remove your e-mail
several things i noted
your using a BSC-621 to feed several units ( dsr 410 X 3 + a 4dtv)
the bsc-621 is designed for one unit meaning that all these units can only use on polarity ( usually channel ) at a time. so if several units want to watch different channels they will interfere with each other trying to change the polarity unless you have the splitter that doesn't alow power passing on all the extra receivers. but they wouls still have to watch what the first ( primary ) unit is watching ( same polarity ). if all the units are trying to control the polarity then you might have a problem.
next you didn't explain how the c-band & ku bands are sent to the units. since you only talk about one coax X 100 ft , i take it to mean that you are running both c & ku through the same coax and you are using the built in 22k of the bsc621.
next amplification - this will amplify everything to include noise .... if you are getting good signal at one receiver .... the problem is elsewhere.
next rg11 -- this is usually used for long runs ... since you have good signal at one unit you won't be able to increase signal strength, just decrease signal loss so the problem is either your splitter or other run of coax... check all connections & your splitter.