If that's the case with your DL1608, I would not want to use that mixer. If I mute a channel, I want it muted EVERYWHERE. A loud BAND from connecting an input to the channel is just as annoying in the monitors as it is in the mains. I'm just asking to further understand, but why do you have the need to mute the input channel to the mains, but NOT the monitors? Peavey made a garbage el cheapo mixer many years ago with auxes being pre-mute. After three events in a small PAC with that mixer, I refused to use it for that very reason (among many others, but that was first and foremost)
What Walter is pointing to is the ability to mute a sub-group or a DCA separately from there input channels. In the case of the XR-18 and now the X32 rack (and on any mixer I use), I have 3 mute groups set up. The first is all inputs (except playback, of course). The second mutes just the mains (L&R), NOT the input channels and monitor buses (don't use this one much, except to check and/or troubleshoot monitors). The third mutes mains and the monitor buses, but allows me to cue up and listen to an input channel in the phones if need be (and I'm not sure this is necessary, but I haven't stopped long enough to see if the input channel cues are pre-mute or post-mute. Did I say that right?? Oh, well...)
Your XR-18 should be able to accommodate any muting arrangement you find necessary.