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

@puffbojie I used to own the Modwright KWA 150SE. I actually had two of them in mono at one point and went back down to one. 

Yes, a preamp will do wonders for you, especially if streaming Tidal or Spotify. IMO the Modwright LS-36.5 DM is one of the best preamps, especially maxxed out with good tubes. When I had mine, I started without the DM, so it was just the single chassis. That already was leaps and bounds better than Dan’s SWL 9.0 SE. the DM upgrade was yet another league higher.

I no longer own Modwright gear but have always been a fan.

The NAD C658 is not that bad of a DAC, especially due to its DIRAC features. Otherwise it by itself is still a clean DAC. While I like BluOS, you also will get much better quality from digital files by having a dedicated streamer. I am partial to Aurender and became an Aurender dealer because of my positive experiences with them over other brands, but there are a lot to choose from. 

I’m fairly certain with your system, you will get greater sonic gain by investing in a good preamp first and streamer second. 

Nobody has brought it up, but quality power will also be a huge contributor in advancing your system’s sonic performance. The KWA 150 SE is a high current amplifier and will benefit from a quality conditioner and aftermarket power cable. 

@puffbojie the ARC preamps you mention are very different from each other. The LS28 is very close tonally and performance-wise to the LS36.5, but the LS36.5 DM version beats it in just about every way. With the right tubes, both preamps can be very harmonically rich while still being quite transparent and resolving. The REF series from ARC are less harmonically rich and more clean sounding, focusing on resolution first. Given where your system is, I believe the LS36.5 or LS28 will be a better fit than the Ref 5.

The Modwright LS-100 is good too, but more colored with more slightly rounded edges than the LS36.5.