Yes, you can add the other DVR to your main viewing TV and use another input on the TV. You will also need to set one of the DVRs to an alternate remote code (or to rf).
Either add another splitter and split the line going to your primary DVR, or replace the 2-way splitter with a 3 or 4 way splitter. Keep the line going to the router (it serves several purposes).
Either add another splitter and split the line going to your primary DVR, or replace the 2-way splitter with a 3 or 4 way splitter. Keep the line going to the router (it serves several purposes).