I have stored the mixer myself and reverted back to the internal speakers on my rack. I was thinking a bit about some changes here when the kids move this fall and with your situation I had a couple suggestions to consider.
1) For the external speakers consider putting the 8 smaller speakers for the scanners in front of the chin of the rack cabinet below the radios they connect to. While you might lose a little space on the desktop you could probably move the console back an inch or so to overhang the back edge to make up for it. You might need a couple new rubber feet or relocate the existing ones.
2) Consider a bracket on the right and left sides to hold the scanner speakers on the sides of the cabinet.
3) How about a shelf on top of the monitors? I have a couple of these, I use one for the DVR on my home cameras above the TV that allows me to view them as well as one for a clock and the streeming device on another TV. You can also use a laptop shelf on a monitor arm.
4) Maybe a couple small clamp-on shelves on the sides of the desk for speakers.
5) Place the larger speakers on their sides and cozy up the monitors to the top of them or even slightly in front, using the monitor arm. Covering a 4th of the speaker is not going to really detract from the listening experience.
On my 3u cabinet I clamped the monitor arm (
Secretlab MAGNUS Monitor Arm | Secretlab US) to the cabinet itself, it appears to be plenty strong enough to hold 2 27" monitors. This arm has a fairly wide clamping base to spread the weight. Before that I found that the included stands on the Acer Nitro's allowed vertical adjustments to just under an inch off the desktop, I went with the arms to clear off the surface for stuffage like my Airpods, cell phone, remotes and a USB hub.