Sounds good in theory but seldom turns out the way we want in practice. I would discourage you from this exercise as i’ve been there and done that and it’ll probably be a downgrade in SQ.
In all likelihood, the Marantz PM5005 (i have the pm6006 and it trounces these cheap chinese Class D amps) has the better pure amplification section than that of the Wiim Ultra. 50w’s of Marantz Class A/B power is greater than 150w’s of Chinese Class D, including the likes of Wiim, in my experience and are sufficient to drive most speakers with authority.
The only budget small form factor class D amp that can do 100w’s @8ohm proper, and good sounding watts at that, is the Marantz M1.
I would suggest that you spend the money on a better speaker. The Mission QX2 is an excellent speaker for the money and you’re unlikely to get better at the price but you can get better if you go up the spectrum. Enquire and checkout the KEF Q3 meta and the Klipsch RP600M II with dealers to get them < 80k.
If you want a floorstander to get deeper and more bass, checkout the PSB Alpha T20 or the Q Acoustics 3050i.
The Mission LX Floorstandrs are a step down in SQ from the abovementioned speakers.