Last year I was experimenting with a design for an audio distortion to be used on line level musical instruments (+4dBu with Zout 100-600Ω by my findings) without the knowledge of impedance, its importance, and how to "use" it. After learning of impedance bridging, I returned to the design and saw that, although it worked as I intended, my impedance was "backward," having a lower Zin (approx 1.7kΩ), and higher Zout (8.2kΩ).
So, concerned about damaging my equipment, I did quite a bit of research, and found lots of information on how impedance affects the signal, and that a low Z input causes loading on the source, but nothing really clear on how the source itself is affected.
So my questions are:
If one were to hook up two devices in this fashion - feeding an audio signal into a load with equal or lower impedance than the source - are there any long term adverse effects on the equipment itself?
Understanding that 10x the source is the rule of thumb, and that something like 4Ω is nearly a short, what ratio to the source would begin to be damaging for a longer duration than something like a plug insertion?
I've learned to adjust my future designs, but am still curious.
Note: This question has been completely rewritten, so for some of the answers/comments to make sense, see the edit history, where you may also find more detailed information on my specific situation, which upon further thought, only brought about the curiosity that is more simply state above, and is mostly irrelevant.