I started with a Bluesound N130 w/ PD Creative power supply, and that fed via coax to a Denafrips Venus 2 and then a Terminator Plus. Overall I was happy with it and for the price, the Bluesound was pretty darn good as a pure streamer. BlueOS has its quirks but overall I thought it was good (on Android devices).
I then recently got a Lumin U1 (from an Audiogon member) feeding the Terminator Plus first via coax then via AES. It wasn't a night and day difference compared to the Bluesound, but it was a substantial and noticeable improvement across the board. Everything improved, particularly soundstage, bass, midrange, and separation. I'm still learning the Lumin app but it's ok, some things I like more about it than BlueOS some things I don't.
But overall I am very content, and I too was specifically looking for a pure streamer as I like having external DACs to allow for changes on that end in the future (if desired).