I'm mixing down a live album from a mono source. The tracks contain guitar, mandolin, vocals, and backing vocals all on one mono track. The audio was captured straight from the tape-out of a mixing board, sent to the recorder before EQ and reverb was applied on the PA. (I made an error at the time of not sending vocals to one channel and instruments to the other.)
While the various sound sources are well enough balanced that I can make the mix sound rather good with some EQ and light compression, I'm concerned that people listening on headphones will experience mono fatigue, where all the audio seems like it's coming from the middle of one's skull.
Is this a valid concern? Are there strategies I can use to mitigate this?