WiiM Pro and Pro Plus will both attenuate their SPDIF digital volume and are bit perfect digital transports. The only difference between the two is the DAC section which for the OP’s purposes is irrelevant. I have both Bluesound Node and WiiM Pro that I use digital direct to my DSP active speakers and attentuate volume in the app. WiiM and Node are both Roon ready as well. Another alternative.
Streamer with variable digital output
In my setup, a Bluesound node feeds a Peachtree Gan1 digital amp/power dac. The Gan1 has no volume control and a digital input only. What other streamers have a variable digital output for compatibility with the Gan1?
BTW, I ask out of curiosity. The Node to Gan1 is a wonderful option for anyone looking for two small boxes and one interconnect for less than $2000.