It might be useful for somebody that
the BTR3 can easily drive the Tin Hifi P1 earphone.
I did not even make the volume control to reach its upper end it is so loud, while my Samsung S7 is not able to serve it in every situation.
Also, the P1 is a niiice little gem,
it gave a completely new life to my BTR3, they are so good together, I was just smirking for almost a whole evening, and the next morning. I will write a review sooner or later, but it is surprising how this relatively cheap setup can approach a flagship headphone with an average audiophile DAC+amp. (Certainly, I use an EQ set to that horizontal S shape.) Yes, in an A/B test the difference is obvious (less bandwidth, less dynamics, worse bass resolution, etc.), but the difference is less than I could ever imagine (except on SBC, of course). Previously I have put down the BTR3 as boring and limited as an amplifier, and it is not worth to get a better headphone connected to it, but now... can't stop listening them when I'm not at home.
By the way, I stated earlier that the BTR3 has extremely bad physical connectivity (range). Despite of my all experience, it was mostly my fault, however, I could call not the second, only the third Bluetooth dongle what I tried as "normal". As a matter of fact, it is the smallest one - the previous (not the cheapest) two sticks
both were just junk, or eventually faulty. So the connection is fairly good now, and it works on longer distances.