Sky UHD is DD+ at best so you're missing little other than the Atmos component, not a huge difference between DD5.1 and DD+
If you're looking to buy a UHD player then get on with 2x HDMI outs.
One goes from the player to the TV for video and the other goes to the AVR for audio. This way you still get the best audio your AVR can do.
Anything 4k like Sky Q and an UHD Blu-Ray player you plug into the TV and then the TVs job is to send audio back to the amp via HDMI. Because the amp only supports ARC and not eARC it supports only standard non-HD 5.1 audio.
Sky Q doesn't offer HD audio, so you don't lose anything without a eARC amp.
UHD Blu-Ray players do offer HD audio, so an amp upgrade is required, or a player with 2x HDMI out if you want HD audio to work. Otherwise you plug it into the TV and the TVs sends the non-HD part of the audio back to the amp.
Anything that isn't UHD yet, like standard Blu-Ray you can connect first your amp before the TV and still enjoy HD audio.
In the long term think about investing in a new amp, its a better and cleaner solution compared to dual HDMI output UHD Blu-Ray players.