Thanks
So if I bought a Bluetooth DAC such as the iFi or Audioengine B1 and connected via optical out/in the Amp would provide the DAC?
But connected by RCA the Bluetooth DAC would provide the DAC?
Yes, if your amp has digital inputs, then it must have a DAC, and if you keep the path digital all the way to the amp, that is the one that will be used. There will be compression if you stream via Bluetooth rather than wifi, though. To minimise the effect of this on the sound quality, your phone and your Bluetooth gadget must both support the same high quality codec (looks like the B1 does aptX HD, but your phone might not).
Streaming via wifi should be more robust than Bluetooth (you shouldn't get the interruptions Darren mentions, compression won't be applied, and it works over a longer distance) but this can be more complicated.
With Android, you can stream to a Chromecast or to a device that has Chromecast support built in. Google also used to make a Chromecast Audio dongle with optical digital output, but this is now discontinued (the regular Chromecast only has HDMI). One issue with the Chromecast is that its streaming protocol doesn't itself support gapless playback, so you'll get slight gaps between tracks unless you use an app that can stitch them together before streaming, like HiFi Cast:
Effortlessly stream music to UPnP/DLNA, Sonos and Chromecast enabled devices
play.google.com
This app, and various others, can also stream to UPnP renderers, which are built into many connected audio devices like receivers and smart TVs. This streaming may or may not be gapless, depending on both the app and the renderer. Since the UPnP renderer built into my Denon receiver isn't gapless, I use a Raspberry Pi as a gapless renderer, which then connects to my receiver via HDMI. The easiest way to do this is probably to run Kodi on the Pi, e.g. with LibreELEC, which includes all the necessary software:
Just enough OS for KODI
libreelec.tv
If your amp doesn't have HDMI, companies like HiFiberry make optical output boards that slot into the Pi, as well as DAC boards if you need them:
If you want to stream something like Tidal to a UPnP renderer, you can use BubbleUPnP:
Cast all your music and videos to TV, DLNA, Chromecast, Hi-Fi, phone and more!
play.google.com
If you have an iPhone rather than Android (or want to stream from iTunes) you'll probably want to use Airplay instead, which is also built into various devices. Since my Apple TV failed, I've been doing this with a Raspberry Pi and LibreELEC, which can render Airplay audio as well as UPnP. I find this is the easiest way to stream gaplessly from my PC, using iTunes.