Thanks for the replies. I spoke to tech support yesterday and apparently the USB port only recognises devices it’s designed to work with and powering routers is very unlikely. Giving it a go would be worth a try but it’s not been tried or recommended/supported by Allen & Heath.
I noticed that the D-Link DIR-510L router is battery powered and is rechargeable. This could be a good option as it has had very positive reviews and is dual band.
I don’t necessarily need a really long range in venues with 200+ people, I’m talking about posh hotels and church wedding services where I need the clutter of cables and equipment to be as discrete as possible.