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Shorting together the two outputs could stress their drivers, depending upon what that driver circuit is.
The circuit of any vaguely designed preamplifier already contains exactly such resistors - in order to meet the output impedance specifications. It's a popular myth on these forums that there's a need to add external resistors.
What specifications are those?
The specifications that any decent preamplifier will come with, output impedance, just as it will come with input impedance specifications.
So how do you know the amp is "decent" and that the the minimum is not zero from an op amp output.
Opamps don't have zero output - and regardless, no preamp will have a problem with the outputs shorted together. But if you want to add extra unneeded resistors, then feel free.
No, but connecting there outputs together is the same as shorting their outputs.
I find your absolute certainty in that statement with no proof, interesting.
Normally this is correct.
Op Amps have about >= 200 ohm open loop impedance, Zol current limited to at least 20 mA. But with error feedback so does Zout. e.g. Aol = 100 dB gain with Acl=40 dB means Zo reduces 60 dB or to 200 mOhms. This means stereo causes current limiting which causes distortion if shorted together.
I believe the opamps that advertise "short circuit protection" have that claim for a reason - the amps that don't have that claim on their datasheets will have problems with short circuits. In the case of this thread, short circuit is any uncontrolled source or sink of current from one op amp to another.
Many opamp preamps oscillate if a shielded audio cable (its capacitance) connects directly to its output, then a series output resistor is added to isolate the capacitance from the opamp output.
