I too have an M8 and really love its sound, especially when driven by the USB B input (hi res).
On balanced outputs, I've gotten balanced cables for two headphones in my stable that I thought would benefit from it (LCD-2, Alpha Dog). I use those cables with the M8, although I cannot claim to hear a difference in that output vs. the unbalanced 1/4-inch output.
I did come across this thread from almost 9 years ago on balanced amps, which has lots of discussion from Tyll Hertsens (at a time when his post count was low, it seems) and others:
I found this post particularly enlightening:
Mick Maloney of Supratek
I often get asked about the advantages of balanced operation-my reply is based on the following:
Balanced/unbalanced is a conentious subject. It comes from the pro audio world where they need it to balance out the noise pickup from very long cables.
True balance involves either using balancing transfomers or turning a Single Ended cicuit (as most preamps are) into a push pull circuit with double the components, circuitry etc- this is the only way to achieve "true" balanced throughout the preamp.
There's a lot of hype about it, with a lot of so called balanced operation being psuedo balanced, which is basically having an XLR socket wired to accept a balanced signal and turning it back to unbalanced.
Personally I prefer Single Ended operation every time- there's an ease and effortlesss about it, wheras true balanced sounds more electronic to me, especially the push pull types of operation.
One area where it is useful is in helping with RF noise in the big cities- it is not an isue for me in my country town isolation, but places like NY benefit from it and in my mind the best way to use balanced is to take it off the output transformer of a preamp, which fortunately we can do with the Supratek pres- it is true and perfect balanced with the minimum of circuitry to degrade the sound.
( there's virtually no circuitry!)
One balancing point in a preamp is all that is necessary- the output transformer turns the single ended circuit into a balanced circuit with two phases and the noise common to both channels (hum, RF etc) is greatly reduced.
Going for balanced throughout is sonic overkill that does more harm than good IMO- it has been a successful marketing campaign by some companies, but it is marketed to sell amps.
What this has taught me is the following (all IMO):
1) I will never recable a headphone with a permanent cord to make it balanced. I'll only buy detachable cables for headphones to use them with balanced outputs if desired.
2) I will never seek a balanced connection for a portable headphone -- it simply adds bulk and offers marginal gains for that type of headphone.
3) Balanced amps are a "balancing act" and as such, I will never seek to buy a headphone amp just because it is balanced, "fully" or otherwise. Of course, if an amp is great because it was designed to work in balanced mode, that is a different story as its designers made that choice. My ears will be the judge.
4) Head-Fi changes a lot over enough time (I don't recognize any of the amp names, manufacturers, or even posters, except Tyll who has totally changed his job description from back then)