Sorry for the late reply!
Regarding listening position and volume, it is very manageable for the 8030s in my situation. My wife HATES anything above 80 dB, and that has kind of influenced me so I rarely go 85 dB. They will be placed on either side of a TV in a small living room at a distance of at most 2m to the listening position.
It is my intention to get a sub, but in time. So indeed the WiiM Pro Plus would be a problem with the lack of sub outs. It seems that the only route is minidsp flex balanced once I have some money, which would then nicely segway into a sub as it is easy to integrate with the DSP capabilities. But price is keeping me from going there just yet. A DAC as a preamp and fiddling with positioning seems the only budget option at this time.