[harley52]

 Not sure if my understanding is right on this wifi thing. I understand wifi goes thru your router and from the router to a speaker or some device.  I guess the speaker has to be wifi capable?

 Bluetooth is line of sight. It's major short coming.

 Airplay/airplay 2.  Airplay 2 goes to Apple TV and Apple TV is capable of sending out a signal to multiple speakers in multiple places?

 Can different speakers have different capabilities or do they all have to be the same OS? Say, I have to choose which system I'll use and then be locked in to that system or is DTS-Playfi a system where you can have for example, one speaker bluetooth capable and another airplay 2 capable. A mix of systems?

 One more thing. Why do I have all three systems on my iPhone and MacBook Air?

 Thanks to anyone and/or everyone that can help me understand all of this.

[brj]

IR is line-of-sight, but like WiFi, Bluetooth is RF based and can penetrate walls, etc..  (Up to a point.)  My Apple TV is located in the crawlspace below my listening room and the Bluetooth based remote has no problems controlling it.

Airplay and Airplay 2 are Apple protocols that ride on top of either WiFi or Bluetooth.  (Bluetooth is peer-to-peer.  WiFi can be, but most often relies on a router as part of a network.)

[Doublej]

Yes, different devices can support multiple methods of transmission and protocols.

A good example is an AVR. Mid levels ones ($300+) can use wired network, wifi, or bluetooth for transmission.

They typically have Airplay, built in internet radio streaming, DLNA/UPnP for accessing music on your computer or network, and/or Chromecast built in.

Bluetooth was designed to be simple point to point such as phone to speaker. Networks are more sophisticated but more difficult to use.