Music streamer with no DAC and no storage?

Bluesound Node 1 (original) only has toslink optical out. Node 2 has toslink optical + coax digital output. Node 2i has 5Ghz wifi, a reportedly better sounding setup for the internal DAC, and supports Apple Airplay 2. If you don't need the faster wifi (I run mine over wired ethernet), Airplay 2 wireless capabilities, and won't be using the internal DAC, spring for the Node 2 since coax digital output has lower jitter than toslink optical.

FWIW, I run coax digital output to my main system, and toslink optical to my bedroom off the same Node 2. It is connected via wired ethernet. Considering that my wifi router literally sits a few feet away from where the Node 2 is, wifi speed would not be a problem.

I also use the Node2, but the OP may want to investigate the Elam Discovery

That’s Elac 

OP stated must have USB output, that rules out all of the Bluesound products.

I would put another vote in for Auralic Aries Mini. Can be found for $500 or so used.

Long time so see Jond, where have you been hiding!