So I'm looking to rebuild the home theater system

Since it is being discussed above...this Arcam review was posted online today:

https://hometheaterhifi.com/reviews/receiver-processor/arcam-avr550-av-receiver-review/ 

whatever I buy will be for watching movies. Movies that are not known for the high sound quality.

Are you saying that the movies you watch don't have good sound quality? OR, because this is for movies, sound quality is not as much of a factor for you? Thanks.

Does anyone know if someone makes an adapter to make an older receiver wifi?

That is what they are for. Many options.

@curiousjim I strongly encourage you to spend time bringing yourself up to date with the 'State of the State' of HT. There are ample online sites to bring you up to date, and with minimal time investment. There are also numerous reviews of all of the receivers being discussed in this thread and those write-ups should give you a good feel for the pros and cons of each unit.

Regarding your previous question(s):

For example, a WiFi adaptor may be unnecessary if you choose to use a Roku, Amazon, Google or Apple device with your TV.

For example, if you have a current TV then you can use the Apps within to accomplish what you are looking for.

For example, most of the current TVs have WiFi built in.

Regarding sound quality:

For me, the soundtrack is the soul and life blood of a movie. With poorer renditions a movie is not nearly as emotionally engaging (sadness, anger, violence, love, etc. etc. require the music to convey the same and to pull at your heart strings).

If a component were more musically competent and emotionally engaging and 'musical' that would be the one I would recommend, without hesitation.

The power ratings (for mainstream receivers) are typically NOT for all channels driven and some companies are much more conservative and accurate with their power ratings.

There are valid and very good reasons why seasoned HT enthusiasts choose higher end / smaller manufacturers over the mass market brands. 

Since you seem to hold on to your components, I advise you choose quality, even if it costs more, over the long run. 

Receivers also lose value quickly, which makes the following option a very good one: step up to a highly regarded, higher end unit that is a couple of years old. 

All the best.

The Amazon and Roku sticks and Chromecast can go direct into your receiver. I'm not sure what capabilities one can control via Apple TV into a receiver, but it can be connected to a receiver.

The issue hinges more on where your files are / what device you are storing your music on. If it can be accessed via your local network (or cast from your phone) then using one of these devices will allow for a much wider feature and control set than a WiFi dongle.