I think you may have misunderstood what balanced ouput actually does... which is... nothing! Effectively anyway. While there was some reasoning behind making balanced amps 10 or more years ago when the electronics available were more limited, and greater power for headphones might have had some benefit, nowadays, in portable devices it is mostly just for marketing. If in a device, such as the M11, they use different circuits for the SE and balanced output, there may be a small difference in the sound only. It's very easy to be fooled into thinking an increase in loudness is an increase in performance. But heck, if you buy a DAP with a balanced output, you may as well use it.
Anyway... more importantly, here's my review:
Enjoyed your review and comparison to the Solaris. I'll be trying the FH7 this weekend for the first time, and brought my Solaris and Phantoms with me to compare. Terrific information as always!