UPDATE: Ok, I listened for about an hour. I think the preamp is needed. (Mine is in the shop.) Why? The dimensionality of the soundstage is much reduced and there is a raw quality to some of the recordings where before there was a smoother and more liquid quality.
In short: I retract my earlier claim that it sounds good. With my relatively inexpensive streamer (but nice DAC), I still want my tube preamp back.
Also, it couldn't play above about 78 db.