The specs on paper for the balanced terminals are great: load impedance - 16-600 ohm, THD - less than 0.04% at 1kHz, frequency response - 20Hz - 80kHz (+-3dB, 32 ohm 10mw), even for the unbalanced headphones output. Not bad, not bad. And in a meantime I revisited the whole balanced thing (being fascinated with it for years, but until just recently it was never within monetary grasp...well, for me at least) - so in short, a balanced connection needs truly balanced architecture between the components (DAC and the AMP here, even if only internally) in order to eliminate ground loop interference, which is the whole idea behind balanced - no humming or other unwanted noise artifacts.
Sooooo, when we throw in the fact that this is Fostex we talk about here and the device is physically made in Japan, plus all the glowing reviews about the A4's performance (and A8 too, I'd think A4BL must eclipse the A8 given the advance of technology and materials since the latter was conceived) - I am starting to plan for real how I will convert my cans to balanced connections, all of them, not just the TH-X00.
I've also been intrigued lately by going for balanced headphones in a different way, but it now seems the A4BL may be the best (and most bang-for-the-buck) way to go. Not to mention that the A4 has an opamp that when upgraded takes it to a whole new level, and my expectation is that the A4BL will share the same opamp design. Which if true, will be just unbeatable combination all around. I can't wait for someone to take a peak under the cover and break the details for us all....how long will that take....I'll stay put for now and actively plan, actively....maybe not for long, we'll see