look i have an M11 - the sound quality that you will get from this is still way better than any phone with a BTR5 - it might be louder if you use a really efficient DAC/AMP like a ifi micro uDSD black label but that will set you back more than what an M11 costs you .... and note i said louder but it wont sound better even bypassing the android layer since it is the phone that is the limiting factor here
the M11 is a pretty decent DAP and now with the updates to its android O/S which allows for the App store usage it now allows you to use UAPP and Neutron or any other software you had on your phone (paid software can be used on any other google based device where you log into the same google account as your phone and you wont have to pay again)
the M11 also has a balanced headphones output with both 2,5mm balanced or 4.4mm pentaconn output sockets - this produces more power so when you have difficult to drive headphones and have a balanced cable for these then it will give those more power than any phone - as an example with the HiFiman HE4xx with a regular 3.5mm cable on a phone i need to run it at full and it still isnt loud enough - replace the balanced cable and i can use it with the 2.5mm balanced output on the DAP at the volume at 100 out of 120 and its loud enough to cause permanent hearing damage if you go any louder - with my IEMs on the phone i can run them at full and they are fairly loud - to get the same volume on the M11 i play at 50 out the 120 and still get less distortion - more clarity and more space and openness and all the audiophile terms that you want to drag around
to me the M11 is worth every cent you pay for it - i had a BTR3 and while the BTR5 is better than the BTR3 one of those with a phone will still be behind in the sound quality (moreso if you have good headphones) because as mentioned above it will be the phone that is the limiting factor .... bluetooth is only for those circumstances where you have to have it unwired but a good bluetooth headphones is likely to cost as much as a decent entry level audiophile grade headphones or IEM anyway - and even using LHDC and LDAC codecs doesnt match wired (believe me i did the comparisons)
Fiio M11 with IEMs - this is how i listen to it most of the time
Fiio M11 with very inefficient HE4xx with a balanced cable - its good enough and is close to being a desktop replacement
screenshot of playstore added to M11
Screenshot of UAPP (USB Audio Player Pro) on the M11 - best software for music playback on any Android device IMHO
maybe i'm biased because i got mine for R7k second hand but that included a Hikvision 256gig microSD card which is fairly big and would normally add R500 to the cost ...... you can use 2 microSD cards in the M11 and its compatible with up to 2TB cards which don't even exist yet
its not the best DAP by any means but it is the best DAP that you can buy new at this price (you might get second hand bargains of other brands but discounting that and going "new for new" this is it at this specific price level IMHO ..... you won't find anything better) and my experience with the M11 is now making me rethink the whole desktop thing too ie i am more in the mind of now aiming for a top level DAP that works as well as a desktop DAC .... something along the lines of a Fiio M15 or Lotoo PAW6000 and one of the crazy priced high end IEMs and that should do for me even as a complete desktop replacement (will cost around R50k in total though for DAP and IEMs together so thats more long term)