Nice thing about the Marantz mid-level AVRs is that they have pre amp outs. So if you find you don't have enough overhead with the built in power, you can add an Emotiva amp or similar later.
Also remember that typical listening happens around 1 watt. You're about 2.5 meters from your speakers. With typical speakers having an 87 dBwm sensitivity, at your seats at 1 watt they'll still have an SPL of (math) dB. I dunno. It'll be louder than talking volume in any case. At 16 watts they'll play 15dB louder, and still have enough overhead for an additional 7.5 dB higher peaks still within the AVR's rated 0.1% THD full range with all channels driven.
The point is, don't get too hung up on rated power. The difference in SPL between 100 watts and 120 isn't even audible. Shop for the other features you want -- Atmos, Bluetooth, needed connections, etc. Power should be at the bottom of your list.
If your Samsung TV does upscaling, then maybe turning upscaling off on your AVR could be a solution if there are problems switching between 1080i and 4K? Don't know. I don't have any 4K stuff.