Placement Ideas for 61 or 88-key MIDI Keyboard With Argosy Halo Desk?

Yeah this is why I go custom.

There is loads of wasted space there since you don't have much rack gear and although the curved profile seems nice, it has the issues which you have just discovered, not much larger gear can fit. Really designed for mixing audio not production work.

Seems you have room to the L/R of your desk for a simple stand. My older setup I just had my keyboards on a custom built stand (was just scrap wood I knocked up into a double stand):

Even tho there is a door behind, it was still convenient enough.

On my desk I have an MCU control surface, Ableton Push and an analogue mixer as well as all my interfaces and compressors etc and a macbook. No more room for a midi keyboard but I really didn't like having to swing around to play simple parts or compose and bounce between the screen and the keyboard so I really wanted to put it on the desk but putting it behind my computer keyboard and moving my controllers was no better since it wasn't ergonomic to play.

I ended up rebuilding my old desk as a motorised lift desk which then allowed me to install a keyboard shelf under it for my midi keyboard. If you are somewhat handy you may be able to do this tho without the ability to lift the desk it can be a bit of an issue.

I used a set of soft-close draw sliders (left over from a kitchen renovation) and made a simple bracket to fit under the desk and clear the bracket for the table lift. I did this after I watched a video on Wintergartan where he did this same thing but something I took from the way he did it was to set the draw back about 1 foot from the edge so when you push it in you have knee room. Just be sure the slides are long enough to bring the draw out.

I also cut a section out for extra knee clearance since it just sits above my knees

I also measured the height of my keyboard and made the draw only just deep enough to allow it to fit to keep it as low profile as possible

As I found, having the desk at a good height so I could slide the keyboard out without it rubbing on my legs meant everything else was too high (monitors, keyboard) so I have a lift setting for "work" and another to play the keyboard which is just 1 inch higher, then a stand position.

If you are handy enough, the draw is simple to install, took me about 2 hours to measure and make it and a set of these slides is about $15, wood is cheap enough so for under $50 you could make an attempt at a draw, otherwise a stand to the side looks doable.

You can measure that distance and find a suitable frame at Eureka because they have a lot of helpful stuff. I recently found a roomy table https://eurekaergonomic.com/office-desk-47-electric-standing-desk-with-drawers-and-detachable-monitor-riser-walnut-erk-ed-i47-wn/ even though I don't have much room in my room. I'm sure you will be able to accomplish what you have in mind.