Some PC soundcards have reconfigurable ports, especially the on-board sound on recent Gigabyte motherboards. For example, one of my PCs with a Gigabyte motherboard can have its 6 audio ports independently configured either as input or output. This also saves having to pull out the PC to see where an audio cable is being plugged into:
I tried this by plugging my speakers into the “Line In” port, chose “Line Out” from this box and the sound came form the speakers as if they were still in the original port.
However, as far as a set top box, Hi-Fi, etc. goes, I am not aware of any with a dual purpose input/output port. In order to convert the port, your Hi-Fi would most likely require a line-in of some sort already, as the headphone port would need to be rewired up to some sort of audio input, e.g. the audio feed between the CD player mechanism and the amplifier circuit.
Just out of curiosity, does your Teac player have a radio? If so, a work-around would be to use an FM transmitter adapter with the iPod and tune the radio to the selected frequency. There are also FM based microphones, although not common now, where one tunes a regular FM radio to the frequency output of the Microphone as a simple karaoke system.