Most of these products will have a fixed sample rate of 48 or maybe 96 kHz. It doesn’t really matter, it will be fully transparent.
$€ 1500 for a 10” sub is a lot of money. You can get something for much less money:
bit.ly
Just let the WiiM do the bass management and volume control, add the DAC, set to full volume, and connect to the B200.
Then get a nice sub, and connect to the WiiM sub-out.
For more than one sub, you’ll need subs with their own DSP so you can tweak them individually. Or add a MiniDSP.