Look I said you were right, but now that you are saying that filters and splitters are the same. They are not.
A DSL "Splitter" is still an inline filter. The line is split, and then one side is run through the inline filter, whereas the other is unfiltered in order to go to the DSL Modem. So if you have an inline DSL Filter it is not "splitting" the signal at all, its just filtering out the the specified frequencies.
This is how I am currently setup. They took the line that was going to my office and installed an inline filter on it at the box. The only downside to this, is if you want to move your DSL modem to another room, you will have to rewire at the box. Also if you want to have a phone at the jack your DSL modem is plugged into, you will still need an inline filter there as well.
Good deal, let us know how it turns out!