The WiiM Pro/Plus has a 2.5mm trigger output jack, not the typical 3.5mm jack. There is a quirk (IMHO) where the turn on single from the WiiM is sent ONLY when music starts playing on the WiiM and not when the WiiM is simply turned on.Yes, if your power amp has a trigger jack. I don't think the cable comes in the box, though. More info in the WiiM manual.
If your DAC has volume control, by having to turn on the DAC separately you now would have a safety check. Turn on the DAC first and confirm that volume is at a reasonable level before starting playback on the WiiM.