Why buy Bluesound Node2i vs. Marantz AVR for playing music from NAS or streaming services?

I currently have a Marantz AVR SR 5010.  I plan to use it to pull songs stored from my NAS and stream music such as Pandora, Spotify.  If that works, what are the reasons why I should consider buying a new network / music server like Bluesound Node 2i or Cambridge Audio CXN?

Is it because

a) My Marantz doesn't have any optical out so all my music will be processed by the Marantz's not so good DAC and output via its analog . If I were to buy Node2i or CXN or others, I will benefit from the better DAC in them or even use an out-of-board DAC like Chord Qutest etc. to improve the sound further.

b) My Marantz doesn't support the latest streaming services like Tidal etc.

Here's rest of my setup:
Sonus Faber Venere 3.0
Parasound P5
Parasound A23
Panasonic BlueRay Player for playing CDs (yeah, I know, it sucks)

Thanks.