The WiiM devices are remarkable value and the HiFi News review of the Pro Plus is worth a read.
The main differences between various models is improvement in the DAC, but you will be using the DAC in the 7000s.
The Ultra is said - by the manufacturers - to have a lower level of jitter on the digital output. Check here WiiM ultra faq

ROON Rock on an NUC across the systems
Sitting room: 218, DSP7200SE
Study: 218, Quad 303, Spendor BC1
Bedroom: Musical Fidelity A3CR, Chartwell LS3/5a
Various Sonos boxes in bathroom and spare rooms