BT using aptX will sound very good. I used to use it in the car with a Helix DSP and quite significant factory audio mods and it sounded sharp, detailed and very easy to listen to.
Trouble for me at the time was my silly android phone kept turning the volume down after 30 mins or so as it was ‘too loud’ (pretty much as iPlops have started doing).
Android might have become more intelligent to realise there is a device and not headphones connected but, at the time it was so annoying that I went to USB audio instead, using USB Audio player app on the phone.
You could also try doing the above and getting USB audio directly out of the phone. Sounds like you might not have set something up right in the above as it should sound slightly better than aptX. I used the USB audio player app and forced the phone to play directly out bit perfect.
Anything from the PC will likely be poor unless you can use aptX on BT or you go into your DAC using USB audio and then the speaker.