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

A Network Acoustics ENO filter on the Ethernet input of the streamer makes a big improvement too.

It is amazing how many people need a course in manners.
emergingsoul, I understood exactly what you you were trying to say. You also could build a NUC instead of the Nucleus for less than 1/2 the price.

Esoul.  you are understandably a little confused about how the roon stuff comes together.  you are not alone.
This youtube is a great help:  http://https//www.youtube.com/watch?v=-ZVcNx-DlIc&t=7s
John Darko does a very good job of breaking it down in all sorts of configurations.

Thanks for Darko link. Seems he is using roon to connect to streamers.  A way of promoting products he may be getting paid for.

he doesn’t choose to keep it simple by using nucleus connected to a standalone dac.  His setups are abit involved.  I like listening to him but always wonder about independence.

From my experience, it really depends on the DAC you are using, and whether you are willing to pay a premium to get incremental gains.

I initially set up my Roon system with a separate streamer (Bryston BDP-2 with upgraded audio card). At the time I was using a Schitt Yggdrasil, and it sounded best using an AES3 connection (this was before Schiit's latest USB interface, so don't know how that compares).

Earlier this year, I bought a Denafrips Terminator and I found this DAC sounded as good over USB directly from the Roon server (Roon ROCK running on fanless NUC using a linear power supply) as it did through the streamer. 

So basically, for the cost of the Yggdrasil DAC and the streamer, I was able to get a much better DAC (in my opinion) that didn't require the streamer. 

There are all sorts of things you can spend money on to tweak the digital playback chain including streamers, reclockers, master clocks, linear power supplies, upgraded ethernet switches, cables and more cables, etc. Many of these things will make an incremental improvement over a simple Roon server connected via USB to your DAC. But you have to ask yourself 1) is it worth the extra expense and complexity, and 2) is it the best use of your budget?