Why do I need an additional player device if I have a Roon nucleus and a dac?

I'm really not sure what you are asking.

If you are asking "do I need a streamer if I already have Roon and a DAC?" then no, you do not.

Actually there is no question. Just some unintelligible statements.

A Roon Nucleus IS an expensive streamer. But you know that.

Your Roon Nucleus can serve the function of feeding directly to the Chord as long as it’s placed close enough to connect with a quality USB cable. You would need an additional player (render) only if you want to place the Nucleus away from your equipment and have the music from the nucleus traveling on you network. The Chord TT2 does not have an Ethernet input so another unit would be required to receive the Ethernet or WiFi signal and convert it to USB for input to the Chord.  You may need something like an iPad for control of the nucleus no matter where it is placed.  

If you wish to place a Nucleus in another room you can use a raspberry pi4 running Ropiee to connect to the DAC. It acts as a bridge. 

Thanks all and especially drrsutliff.  Streaming equipment can be abit challenging to understand, and it don’t need to be.  So easy to make a purchase mistake, etc.