i'll give you another example, if i put a dac's fiber optic out into an amp, and plug in balanced headphones/speakers into the balanced out of the amp... is it still balanced? short answer, yes.
If you directly connect a fiber connection (TOSLINK, I assume) to an amplifier, it wouldn't make much sense. That amplifier would still need an internal DAC to convert to an analog signal for the amplifier. Who knows if the analog output from an internal DAC would be balanced?
I guess I'll throw a monkey wrench into this discussion anyway -
There is a school of thought (quite vociferous from some) that distinguishes between
balanced and
differential. In this convention, balanced means the ability to connect and input/output to balanced cables. So IOW, if you are dealing with real-world recording and performance, if the equipment in question is able to connect through long runs of balanced cable, then the equipment is indeed
balanced.
On the other hand, what we are really interested in with headphone electronics is whether a DAC or amplifier circuit path is
differential. A differential circuit removes all common mode distortion. In addition, typical voltage swings and slew rates (voltage acceleration) are doubled. In that case, the connections become secondary (assuming we are not interested in hundreds of feet of microphone cabling) and the circuit itself becomes more important. Now, an amplifier can either have balanced connections, or not … and it could still be a fully differential amplifier. Or, it could be a single-ended amplifier with fully balanced connections.
The purists among us would favor a fully differential DAC and a fully differential amplifier, with balanced output on the DAC and balanced input and output on the amplifier. The question is, where does the benefit really exist? In the amplifier circuit or the connections?
