Splitting output? Sure can. You can also split AND diplex your 301's output to multiple T.V's. The DPP Twin won't interfere with that at all.
Diplexing that output may be helpfull depending on your home/wiring. You actually could diplex and split your Sat feed all the way to your "cable box".
Place a splitter behind your reciver with the 3/4 out going to the "in" of a 2-way splitter. Port one out of your splitter will go to the UHF port of your diplexer. Port 2 out of your splitter will go to your tv. SAT of your diplexer will, of course go to your SAT "in" on the reciever.
Now we follow your single cable out to a cable box? (unsure of your set up) Place the end of your cable on the single port side of your diplexer. SAT will go to your ground block or your sat feed line coming from your dish. UHF will go to another splitter to multiple TV's.
You can also get yourself a DishPro UHF upgrade kit. That will allow you to take your new remote controll to other rooms in your house and still operate the reciever.
You probably already realize this but, you won't be able to view different channels on the 2 or more tv's coming from that 301R.
When in doubt, run a hard line
Good luck sir!