Do I need a dac


So kinda new to this streaming .my question is I have a lumin t2 hooked to an audio research reference 5se should I also have a dac to get better sound 

tunawishing

Not really! The DAC in the Lumin is high quality! Using an external DAC is likely to be a sideways move! 

Roon will not improve your wallet. Some report that it comparatively hurts the sound quality. I didn’t notice that, but it is not for me.  I have never read that it improves ANY SQ.

An external DAC could be worse or better depending on your taste, the resolving power of your system and spending ability.  Most likely diminishing returns  make it too expensive for most.