A balanced headphone cable serves mainly 2 things. Eliminating the possibility of talk throurgh by eliminating the common ground and doubling the voltage swing with positive/negative signal rather than 0/positive.
It has probably something to do with processor load. A wav file does not require processing power to unpack it. The Colorfly C4 does not support hires flac as the processor can't cope with the unpacking so only support wav. Same with other purist players. On the DX90 I am unable to hear a difference but that does not mean it's not there or that some can hear it
Lurker fw is cleaned up by removing not needed bits and some versions have different font but all are based on the iBasso fw.RockBox has a lot more options than the iBasso Mango player. Some prefer it on sound as well, I have not tried it, am perfectly happy with Lurker 2.1.15