Are higher end preamps worth the investment when you are only streaming Tidal & Spotify ?

Sounds like a decent Dac/Streamer combo to replace the NAD may be a good idea. 

Yeah, I’d wholeheartedly agree with that.  Here’s a great streamer you can also load your CDs into…
https://www.usaudiomart.com/details/650011170-innuos-zen-mk3-1tb/

And you can add this excellent Denafrips R2R DAC…

https://www.usaudiomart.com/details/650012161-denafrips-pontus-ii/

And with your budget you could even add this Denafrips Iris DDC that’ll let you take advantage of the DAC’s superior i2S input…

https://www.usaudiomart.com/details/649988598-denafrips-iris-ddc/

Using this simple HDMI cable, which is what I use from my Iris into my DAC (and yes, get the 0.5 foot length as the shorter the better for i2S)…

https://www.monoprice.com/product?p_id=13578

This would be one kick-butt streaming system on the relative cheap.  Hope this at least gives you some food for thought, and best of luck  

I don’t see anywhere where you list the room dimensions and/or characteristics that requires Dirac to make it sound good — am I missing something?  There are lots more options than your NAD, and between its mediocre preamp and streaming capabilities you’re probably paying a very high price in performance just for Dirac.  With a budget of $10-$12k and considering the quality of your other equipment you could certainly do much better.  What’s up with the room???