Hi Chuck,
It’s a bit of a weird setup.

The bottom keyboard is a Yamaha p121 piano. ( 73 keys) with the optional 3 pedal unit unit and the p121 piano stand.

The sx 900 sits on an old glass hall stand ( table basically) that just happened to be the correct height and length behind the piano. I covered it with a black sheet instead of just having the clear glass showing, along with all the cables and junk.
The sheet hides it all nicely.

I can actually slide the sx a bit further forward if I want to,.

I’d even looked at using a small book case to put sx on, and covering with a black sheet, just happened to have the right size piece of junk, ( hall stand) sitting in the garage wasting away.

Even a book case would have been safe enough , the piano wedges it against the wall , so it can’t topple.

P.s. the p121 doesn’t have 5 pin midi ports , so I use my laptop as a midi interface between p121 and sx 900 via USB. I could buy some sort of dedicated little black box to do it, but I have my sx connected to laptop most of the time anyway, so haven’t seen the need to buy something extra.

I use the p121 as a controller for the Sx900. Normally I mute the p121 piano sound when I play in arranger mode. The weighted keys make the sx piano sound nearly as good as the p121 piano, so decided not to have the hassle of a complicated midi set up.
Sustain for sx900 I actually get via the p121 sustain pedal. I then have the other 2 pedal connections for the sx itself. One I have set for registrations, the other one, I’ll possibly end up using for expression, if I can get the old Technics pedal working with it.