You're correct about the splitter but if you currently have no splitter...you're in a much better situation.
I have the TM3402 and its DOCSIS conked out last week. I had to connect an older DOCSIS and the conked-out TM3402 because its telephone side still works. However, to connect 2 devices, I had to replace my 2-way splitter with a 3-way. More splits...more degradation.
However, you have no splitter so you won't have as much degradation with the 2-way solution.
Just make sure to connect your Internet modem to the lesser leg of the splitter (3.5 dB).