That's exactly the setup I've had for the last three years In this the two min-jack sockets are wired in parallel to the plug so if you plug two outputs into the sockets then you have directly joined them together. Which is really designed to feed two pairs of headphones from a single socket. The kind of thing i am advising against is something such as this. If you have a switch so that only one output is connected at any one time then you avoid all that risk. In some circumstances an output can appear to be a short circuit which will totally knacker the signal level and in a poorly designed output stage can destroy the electronics driving it! If you plug an out put to an output it will be totally missmatched and will more than likely result in a greatly attenuated signal level compared to if it was plugged by itself. Outputs by and large are low impedance, inputs are high impedance. This will have an impact on the signal levels depending on the impedance of the outputs. Something they were never designed to cope with. Basically a splitter in reverse joins two OUTPUTS together.
