The speakers have a high sensitivity rating so 50W into 8 ohms (55 for the Yamaha) should be enough for casual listening. If you wanted to play it loud, you would need to double the power rating. The Denon is rated at 85W into 4 ohms, and while I don't see a 4 ohm spec for the Yamaha the amp is rated down to 4 ohms so either amp should drive those speakers ok.
Big difference in connectivity options though. The Denon has multiple optical and analogue (RCA) inputs so it supports more physical devices. With the Xbox connected to the TV you can use the optical out on the TV to connect to the amp. There is no network, wifi or bluetooth, so you would need an external device to stream your music to the Denon. Something like a Bluesound Node could act as a streaming source, which handles Spotify, Tidal and networked files (although there are cheaper options as well). The Denon has bass and treble controls up front if that is important to you.
The Yamaha has only one optical input and one analogue input but supports bluetooth and wifi. You can also use the optical in for the TV. It has support for Spotify Premium, but it does not mention Tidal on Crutchfield. Music files on a PC or other device can be streamed via Musicast and I believe Spotify would be handled through the Musicast app on a mobile phone.
It does mention that music can be streamed to the WXA50 via bluetooth, so if you have Tidal on your phone you could stream to the Yamaha via bluetooth but there may be quality issues converting high-res streams to bluetooth. I'm hoping that someone on the forums who uses Musicast can jump in and explain how Tidal could work with the Yamaha.
EDIT: I see Tidal listed on the Yamaha web site, so the WXA50 would give you an all in one solution. They give a 90W into 6 ohm rating (Crutchfield had listed 4 ohms) but if you don't plan to drive the amp hard and give it plenty of ventilation, it should handle the 4 ohm load ok.