Most op amps are short circuit proof but it is not a good idea to short the output anyway. However, in most cases there will be a resistor after the op amps output which means it's usually ok in practice. Shorting pin 3 to 1 at the receiving end but leaving pin 3 open circuit at the driving end would be best but in any of these cases you are no longer using a balanced connection and the unbalanced should be preferable.
As an aside here, many balanced items work unbalanced internally and use a "line receiver" and "line driver" IC to convert the unbalanced to balanced at the source and then convert the balanced back to unbalanced at the receiving end. These IC's consist internally of usually a 3 op amp circuit. Sometimes in fact 3 op amps are indeed used at each end in place of the specialised chip... results are about the same.
My point is? Well in all such equipment using the balanced input and output means in effect taking the unbalanced signal and then feeding it through 3 op amps at each end! Hardly minimising the signal path....
DAC's tend by their nature to have true balanced outputs anyway (even if no balanced output is provided in your DAC the DAC IC usually works in balanced form) and so in nearly all cases a DAC with balanced outputs IS truly balanced, but the same is not true of pre amps and especially power amps. It is certainly possible to do both in true fully balanced form but it greatly adds to cost and complexity and makes things a bit awkward to use them unbalanced so the "cheat" method which adds the 3 extra op amps at each end is much more common.
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