Through the set ups in my home, I have two WiiM pro plus units and three ultras. I love the WIIM products. Two ultras are going through external DACs (Benchmark DAC2 HGC and SMSL DO100). All sound really good to me, but the two going through external DAC’s sound a touch better, especially the benchmark. It is also set up in a higher performing system.
The main difference I found between the WiiM units, had to do with Wi-Fi connectivity. In one set up in an upstairs bedroom far from my router, I was getting drop offs and connectivity issues with the pro plus. When swapped out with the ultra, those issues disappeared.

