The MX822 looks like is is all XLR, so that wont work.
The RX1602 would probably work. I didn't like that it had no XLR, and it only has 1 monitor send, where the SM-10 has 2. I wanted at least 2, and they are stereo sends, so if you send in mono you can support 4 sends. Before I bought the Samson I was using an old desktop Behringer mixer that had 2 Aux sends, so I was set up that way. If you dont care to have tabletop, you can get far more mixer for your money than going with only rackmount.
Yes, that is basically how it works. You run your amp/preamp into a channel, and then the outs into a poweramp. The Monitor send goes to the input of your effects unit, which then comes back in stereo on another channel. The Monitor send on the channel your amp is connected to basically becomes a signal send volume to the effects unit, and the volume on the channel your effects return is coming back to becomes your effects mix level.
The KTG 2100 is basically their copy of a VHT 2150 or 2/90/2. It has a negative feedback control instead of depth, but I modded it to have a depth control, so now it has volume, presence, depth, and negative feedback controls per channel. It is pretty massive.