Stereo receivers and integrated amps don't sell nearly in the numbers of AV receivers. Consequently, one ends up paying much more for much less. I don't see their allure except for niche situations like a purely analog setup.
Denon for movies and Marantz for music is 100% poppycock. In the £500 price bracket, they are nearly identical. The minor difference in amp power will be inconsequential. Pick whichever gives you the features you need or hits price point you desire.
For streaming functions, probably best to get a Chromecast or Amazon fire stick or Roku.
Since your equipment chain is short, lip sync should not be an issue. That said, or doesn't hurt to have the feature.
Last but not the least, your speakers will last for decades. The electronics, not so much. When moving too this side of the pond, you could keep the former and ditch the latter. Spend accordingly.