Assuming that your POTS line will become a dry loop DSL only line directly connected to your modem, you'll have to disconnect the internal house wiring from the outside circuit and plug it into the MJ+.
In essence, your house wiring will be isolated from the Dry Loop, hence you will not require any filters at all on your phones.
Should your MJ+ somehow be inadvertently directly connected to the outside line all sorts of bad juju would happen, probably blowing out the MJ+ and necessitating a service call for your phone line as well.
One thing I'd worry about is how many phones you plan to plug into the house wiring and their ringer equivalency or REN numbers. If the sum total of those numbers is higher than something like 4, you stand another good chance of blowing out the MJ+. The RENs are marked on the bottom of each phone's base unit. Just calculate the algebraic sum, including any telephone answering devices or fax devices you may plan to connect.
Just to eliminate any confusion I've uploaded a schematic of what your setup should look like. NOTE that the Dry Loop HAS TO BE DISCONNECTED FROM THE HOUSE TERMINAL BLOCK.
Set it up like this with a reasonable number of handsets with low RENs and you should be good to go. One way to really cut down the REN is to use a multi-handset cordless phone with a single base unit.
Hope this helps. Happy holidays!