My wireless fiber optics modem doesn't allow to split bands either, but in advanced settings I found an option to split and name them differently. System advised against it claiming that automatic choice is better, but it always picked 2.4GHz since it was the stronger signal.
2.4GHz WiFi channel is 3.5 channels wide - resulting in only three non-overlapping channels. My microwave operated on one of them leaving me very susceptible to interference (frequent drops with airplay), while 5GHz seems to be immune (in spite of weaker signal).
Check advanced settings or search forums.