Port>digital out> DAC>Analog Out> Analog input on preamp. 

Also note that if all you need is streamed music from the port and one other source connected to the line in jacks on the port, the preamp/DAC become redundant except psychologically as more boxes.

The convenience of volume control on the Port from your phone/device is a good way to get over the psychological need for more boxes ime

You can have that convenience WITH more boxes downstream of the Port! In my case I am at a stage in life where lesser the boxes the better. I have passed through the more boxes phase, so I am no one to criticise it.

Guys please provide some input here. I have a Prep and power amp. The port is sandwiched in-between the pre and power with my powered sub getting its signal from y connectors on the port output. Here is my thing. I have thought about outputting the ports digital out to my Pre amps built in DAC but I do not see the point as in the current set up I can use all post pre amp sources (CD/Tuner/Turntable) on the line in of the port and thereby be able to stream everything to the rest of my Sonos ecosystem. IF I stick with this configuration I have been using both pre amp and Sonos to adjust the volume. I find it works better (for fine tuning) if I share the volume control between the pre and port however the simpler way if I am of the understanding would be to have the port be the sole source of volume control. If I do that I still need to set the pre amp volume to 0 db (rated output)? Or am I better off just setting port to pass through (unless I am streaming directly from it)? A little long winded sorry. Thoughts