I've used this mixer for a few years and here are some things that I really like about it.
The aux sends are indeed mono, however, I use the 2x stereo channels for stereo returns. This is common practice to only use a mono send for a delay and reverb in the hardware world even for a stereo signal. I use a Sarajewo delay for aux 1 and return the separate delay taps to A and B to get the widening. Sound amazing. For the 2nd aux, I use an FX Aid as a set and forget verb and change up the algorithms to get different timbres. Also sounds great.
Since the aux returns are freed up on the top left corner of the mixer I use one to play ambiance, in my case, a vinyl crackle from 2hp loop. You could use it though for a sub-mix. You also have another set of mix inputs for an additional sub-mix.
The A-B switches effectively double your inputs and I usually will attenuate one of the inputs externally and use the gain control for the other. Sometimes, it's not needed if modules just happened to be balanced already. An example setup is I use an Erica Hats D in the A input and control the gain there, and for B input I sub-mix Erica Drums1, Mosaic 1u Hats, and Patching Panda hats into a Mosaic 1U mixer and that mixer out goes into the B input. I can just adjust the individual hats volumes on the 1U mixer and flip to A to mute the Mosaic hats group if needed.
Each channel has CV over its VCA and panning. I use an inverted envelope to "duck" channels where needed. This is tricky though cause unless you have an envelope with inverted outputs already you have to do some things to get it to the right voltage, shape etc. Something to note is the Channels expander has CV over the gain of stereo channels it adds in addition to the VCAs, which is not the case on the main module. Comes in handy.
You can use the cue output as a send too and do tricks with that.
A huge feature only found on a few outboard mixers is a master fx send and return. I personally have a mastering chain consisting of Happy Nerding TriTone for EQ and saturation, WMD SCLPL setup for DJ style filtering, and a WMD MSCL compressor set as a limiter.
Lastly, is the ability to run line-level gear in conjunction with modular gear without the need for attenuators or line-in modules.
I also use the DB25 expander for the individual outputs, though, one downside is that the outputs are pre-fader. Good for samples, but not so much for capturing performances and being able to mix them in the DAW later. I just use the stereo outs of the mixer which go through both the main module outputs and the DB25 outputs at the same time, which means cabling can be flexible and you can record with a secondary backup device too.
My wishlist for it.
-The current Mutes module adds mute buttons, but also CV over the aux sends on channels 1-4. I just want a 2hp module that allows CV over the aux sends which is totally doable and maybe even DIY as WMD has mentioned I could ask for the pinouts.
-Clickless muting for the Mutes module. On both the Mutes and the Overseer you can get clicks. I'm not sure what goes into this, but I know it's possible because Happy Nerding has a Mutes module that doesn't click as it only engages or disengages at the zero-crossing or fades in and out (IDK, I'm no EE).
-This is personal, but I would like a set of inputs like the mix-in to sum post master inserts.
-Lastly, sometimes I have to attenuate modules before they go into the mixer because the level is so hot it's clipping the mixer already with no gain. I suspect this is because of the amount of gain they have dialed in to accommodate line-level gear. Would be cool if this was switchable on the back (I hope I'm not missing something on this).
All in all, it's pretty incredible how much went into this mixer. It just does so much more than its size lets on and though it's a good amount of HP in the rack, there's no other way to get this much functionality in that same space.
I highly recommend it.