I have a couple of reasons to play a second audio file(s) continuously under the main output, or have two tracks playing independently but together in the playlist. One reason we do this is we transmit a continuous super-audio tone (21kHz at -24dB) as a pilot tone for downstream sensing equipment. A crude way is to use a cart slot and load a very big file. It's ok but not really suitable for long periods as the file is too big. A neater way would be to have a 'repeat' or 'loop' toggle option in a cart button, or(better) to be able to create a loop sequence of cart files. I can see other uses for this secondary file approach, such as broadcasting pilot tones during split ad breaks or news opts (to trigger downstream affiliates), and this requires slightly more subtle scheduling or macro triggering than currently available from the main playlist.