With DSL assumed, the best place for the filter built into the modem is at the entry to the house. Then you do not need any other filters. This may be an inconvenient place to receive your internet signal but given than some DSL modems only have one output, you may be able to run one RJ11 cable to a switch where you will have 4 or 7 outputs plus the one input--they are cheaper than routers. On a switch all lines are equally connected and you do not need a router's censoring with DSL.
Another thing that can be a problem is that some phones (an unpowered one in my case) need the correct polarity to work because they use the 120 VDC from the phone company at low current. If you must reverse the polarity the cheapest way is to use one extra cord, coupling the two pieces with a dual socket, typically used to have 2 outlets from one. Each cord reverses the polarity--look at a flat one and the tracer thread, often black on one outer wire.
Another possibility is that you have 2 phone lines using more wire connections (all 4 wires) and you are grounding the wrong one inside the receiver--it shouldn't. You would need a 3-way jack with line-1, line-2, line-1&2. Use line-1 (or line-2 if that is your Dish phone number) to the receiver and 1&2 to the reset of your phone system.
Guess a little more info on your phone system would eliminate some/all of these idea.
-Ken
P.S. written before your reply, so most ideas go away. -K
