I am running a Behringer XR18 to a Bose L1. I use the Left aux output (xlr) on the Behringer to the guitar line in to the Bose (1/4"). I currently run the female xlr to a TS. Should i use a TRS instead? Or will that bring unwanted noise or be unbalanced?
You may use either a TS or TRS to the line/guitar input of the Bose either way. The input is probably TS since it is set up to accept an instrument level or Line level and nothing indicates that it is balanced input.
If you send a balanced signal through a TRS jack to a TS input, the second signal will be sent to ground and not used.
If the Bose does accept balanced signal through TRS, then you can send a longer run with less noise by using a TRS, but otherwise your current configuration should work fine.