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Hi Again Rich Powers:
I just carefully re-read your opening message and see a question no one else asked.
Are you sure the output you called a “headphone output” is really that, or could it actually be a “line output.” The expected technical difference between the two is in PhilB’s note.
Then later on, you mentioned you weren’t sure about how to interpret the impedances that have been tossed around, and this dislodged some deep buried information I’ve not used in awhile, which may give you a frame of reference:
There are two types of impedance inter-connections: matching and bridging.
An example of matching is when the output impedance must exactly match the input impedance, as with an audio amplifier (8-ohms) or a transmitter’s RF output (50-ohms).
But today most audio connections use the simpler bridging method, and the rule of thumb is simple.: A low impedance can drive a higher impedance so long as the higher impedance is at least 5-times greater than the lower source impedance.
So if the source output impedance is 1,000-ohms, it can drive anything 5,000-ohms or higher. That’s called “bridging.”
One of the earlier notes did touch on this, but simply used slightly different words to describe it.