I haven't tested this myself, but people often attribute increased/better SQ with firmware updates, and the hardware hasn't changed there either. I guess HOW the gear handles those bits is different depending on the firmware or app.
I actually do use Neutron on my HTC M8, have not done comparisons in eons, but I did compare years back and liked Neutron better. I actually don't download music on my phone these days, use a Pono for that, but I often stream WFMU.org. They have an app that includes a pop up player, or you can stream a 126mb signal from the web page. I find the stream much better sounding than the pop up over my phone, but that could be the signal differs between the 2 streams of the same radio show, the 128 being a higher fidelity signal (I don't know this to be the case, but I do suspect it).
I'm sure you'll be fine with Poweramp, though...