I have the WiiM Pro Plus and much more expensive Matrix Mini i-4 streamer, the DAC of the latter is more capable, more better sounding but I wouldn't say it's night and day. I think it is the same with higher end models, there's the diminishing returns. Matrix Mini i-4 streamer is pitched against the Eversolo DMP A6 and the sound quality is roughly on par. I haven't tried it, I think both Matrix and Eversolo and WiiM Ultra can operate as a preamp, mine has RCA line input. Ultra has phono RCA input.
I'd opted for the Matrix because the price has been greatly reduced, about £170 cheaper than the Eversolo. The price on the Eversolo has also come down, standard version originally £850 but if you check out on AliExpress it's fallen to about £650ish or less.
If DSD isn't your thing, I think you're better off with the WiiM Ultra if you're thinking to bridge something of value with sound quality.
The Ultra and Matrix allow USB storage but to access the contents you need your mobile and for most of us it isn't an issue but somethings I'm old school and I prefer direct access rather than fluffing about with the mobile. That is why I got another digital transport, which allows you to play your locally stored music directly into the DAC/Streamer device, works really well with the Matrix.
I also have the same combination with the Eversolo Z8 DAC.
My JF digital transport is Android OS based, and I have Tidal, Spotify and others on app and this negates the use of a streamer, if you prefer to save costs and just have it aligned to a better quality DAC. If you don't mind Android that's fine otherwise align it with a streamer DAC.