Transferring different signals at the same time via rf
A TDM (time-division multiplexing) approach would be the most straightforward method to implement. The transmitter would send out frames of information, each containing one audio sample for each receiver. The frame rate would equal the audio sample rate.

--+-----+------+------+------+------+------+------+------+------+-----+--
  |frame| ch 0 | ch 1 | ch 2 | ch 3 | ch 4 | ch 5 | ch 6 | ch 7 |frame|
--+-----+------+------+------+------+------+------+------+------+-----+--


Each receiver would synchronize to the frame flag and then pull out its assigned data. It would transfer that data to its DAC at the next frame flag, simultaneously with all of the other receivers. The only timing skew would be the difference in radio propagation delay to each of the receivers; less than 1 &micro;s if they're all within 300 meters of each other.

A data rate of 60 kbps (I assume that this is per receiver) suggests a rather low audio quality; e.g., 8 bits per sample at 8 kHz sample rate, which is comparable to "telephone grade". This requires the transmitter to operate at about 500 kbps.

If you want to produce something more like "broadcast quality" or "CD quality" audio, you're going to want at least 16 bits per channel at a sample rate of 32 to 48 kHz. This would be 512-768 kbps per receiver, or an aggregate rate of 4-6 Mbps at the transmitter.