You might want to compare the ASR review of the WiiM Amp Pro and the ZA3.
This is a review and detailed measurements of the WiiM Amp Pro networked streaming stereo class D amplifier. It was sent to me by the company and costs US $379. The package is minimalistic in nature and matches the "non-pro" version of the amplifier. The volume indicator is that set of LEDs...
www.audiosciencereview.com
This is a review and detailed measurements of the Fosi Audio ZA3 stereo amplifier with balanced XLR inputs. It was sent to me by the company and costs US $149.99 with 48 volt power supply. The amplifier has really dressed up from its earlier origins of common enclosures in budget class...
www.audiosciencereview.com
A single ZA3 has about zero benefit over the power amp stage of the WiiM Amp Pro. In particular the load dependency is noticeably worse for the ZA3 due to missing PFFB. SINAD is vastly superior for the WiiM Amp Pro. Even the difference in power into 4 ohm speakers (117 W vs. 140 W) only makes a difference of <0.8 dB SPL!
If you are after two ZA3 in mono mode, the difference in power is a bit higher, but the sound quality won't improve.
On top of that you need an external USB DAC that betters the WiiM Amp Pro. Looks like a complete waste of money to me.