Most likely the best solution is to share your music using a protocol called UPnP. Here’s an overview of UPnP from Cambridge Audio - link. You also might read another term - DLNA - mentioned in the same sentence as UPnP. DLNA is a set of guidelines established by consumer electronics companies for interoperability between media devices. However, it uses UPnP to implement those guidelines. You can consider them interchangeable for streaming purposes.
The UPnP protocol is lossless and bit perfect. Virtually all the streamers on the market use this method for control and playback. Even if you don’t follow the approaches I outline below (for example, if you decide to add the Bluesound N130 to your system), I highly recommend reading the overview to understand how this type of setup works.
The good news is that you most likely don’t need to buy anything to try out streaming with UPnP.
You will need to connect the BDP-105D to your network. See p.44 in your manual for details. This will turn your Oppo into a UPnP renderer.
The easiest way to experiment with UPnP is to use a Windows PC and download an app called Stream What You Hear (SWYH) - link. Follow the getting started guide to set everything up for streaming playback - link. I also highly suggest turning off all your system sounds since they’ll play over your stereo. Then connect your external drive to the PC configured with SWYH and use your favorite player to browse the files on your external drive and play some music. If you selected the Oppo as your renderer, the music should stream from your PC over the network to the BDP-105D.
If you feel you need something more advanced than SWYH, then setting up a UPnP server to share your music with the Oppo would be the next step. This can also be done with a Windows PC. If it has enough capacity, I recommend copying the music off your external drive and into the ’Music’ folder on the PC. This will simplify setup.
To turn any Windows PC into a UPnP server, you need to enable ’Media Streaming’ from the Control Panel. Here’s a guide - link. This will share all the files in your Music, Pictures, and Video directories using UPnP.
Now you can download an app to your mobile device to turn it into a UPnP control point where you can browse your shared music as well as stream from services like Tidal and Qobuz. I use BubbleUPnP (link) on my Android phone and mConnect HD (link) on my iOS devices.