AUX to XLR cable vs direct box
There is the assumption that if most gigs have clean sound without a DI box, then there should be no problem. Until the day comes when you have hum in your signal and maybe buzzing noises from stage lights. It is worth it to have a simple passive DI box on hand just in case. These have an isolation transformer with a high-impedance input and a 200 ohm differential XLR output that makes it immune to noise, even if it is a 200 foot run to the sound tower. This article helps with the history and adds more details.


  Purpose:The direct box takes a high impedance, unbalanced signal
  and converts it to a low impedance, balanced signal. This allows the
  signal to be sent over long cable runs with significantly less signal
  loss (especially in high frequencies) due to the lowering of the
  impedance, and greater rejection of interference due to the benefit of
  common mode rejection in a balanced signal. Furthermore,
  the lower impedance (around 600 ohms is normal) allows an
  insignificant load to the input of a mixing console or preamp which is
  also designed to accept input from low impedance microphones.


There are battery powered versions for microphones that need phantom power and/or a gain boost as well. You may not need a DI, but if you do and you have one it can save you from a disastrous gig.