Alex....in one system I run the Dragonfly Red in the same fashion that Donnie mentioned. If you are using an iOS device, make sure to use the Apple camera adapter kit and not the regular USB adapter. It has way better galvanic isolation and will allow you to keep your device charged while you are using it.
Option #2: First off...I would avoid Bluetooth if you can. It compresses and degrades the sound the too much. Everything sounds too thin and you get alot of smear.
For an inexpensive solution I would buy a Google Chromecast Audio device and tie it in to your home WiFi network. Way better sound, and it will let you stream up to 24/96 Hi Res. files from your mobile device. All you have to do is download the Google Home app, set it up, and make sure you have the “Full Dynamic Range” setting enabled. You will go from the 3.5 mm jack on the device into your amp with an adapter cable. You can pick up the CCA on eBay for like 50 bucks.
FYI.... they were discontinued by Google in the beginning of 2019, so they are a bit harder to come buy. The device uses a combo 3.5/ mini Toslink output jack....so if you want to go into a separate external DAC....you can. You will get way better sound than using Bluetooth.
One small hiccup... If you use an external DAC and run the CCA with a Mini Toslink adapter, all 24/96 files (and higher) will come through with an occasional click/pop. It’s basically the limitation on the device. There are work arounds, but that is another topic of conversation.
If you use the internal DAC of the Chromecast Audio (CCA) via the single ended out with a Y cable, you will be able to play 24/96 files and get full sound. Any file higher than that just gets down converted to 24/96.
I run my CCA via Mini Toslink into my external DAC and just play music avoiding the 24/96 files. It’s no biggie and I still get great sound through my external DAC.
What’s nice about the CCA option, your mobile device is no longer tethered. You can move freely around the house and change music at will. Here are 2 quick John Darko videos that will give you a better idea of the device...
https://youtu.be/4m8v7xjWu60https://youtu.be/qX2LbNfMAS4Hope this helps.
Dominick