Streaming directly to my power amp on my second system for years. In my First Second System, I had an amplifier with gain controls and a Denon CD player that also provided some limited volume control. Plugged the CD player in direct to the power amp. Great sonic result and it’s simpler to manage. Even simpler now with streaming.
Since the OP mentioned a Marantz preamp, will also say that I’m very happy with the sound of my main rig setting my AV7001 in PureDirect mode. I need a preamp on my main rig because of all the input devices to control. But it just seems to make sense that if I can cut out a layer of electronics, I’ll get closer to the actual source signal. This seems analogous to hearing a Direct-To-Disk vinyl record vs ones that were made mixed and mastered the usual way.