Recently I've been inspired by this thread and the other about in-ear monitoring. My singing has been slightly pitchy because I've been unable to hear myself properly when I'm outdoors busking with my amp facing the audience. Today I spent 5 hours to finally arrive at a really good but unorthodox monitoring solution!
My main amp is a Roland AC-33 and not a Loudbox Mini so the cabling may vary but here's my solution:
I stereo out my amp through aux into a quality Sony XB20 bluetooth speaker (pictured below) and put it on my music stand facing me.
This is particularly tricky in my situation because I need another stereo out into a separate column PA (Laney AH4x4). What I did is to sum the AC-33 left + right into an aux out, attach a splitter at that end to get 2 stereo outs, and aux in to the Sony Bluetooth and also the Laney AH4x4. This is an extremely low cost and convenient solution with amazing sound quality so it was worth the cabling. For the Loudbox Mini which has an XLR out, you probably need to find a way to double the mono signal to make sure the bluetooth speaker uses both cones. Hope it helps!