Prophet 5/10 desktop: 20.75" wide
Rev2 Desktop: 21.6" wide
Prophet 6 desktop: 21.25" wide
OB-6 desktop: 20.75" wide
Heights range from 7.4" to 7.9", or roughly 5U.
...
The available width of a 19" rack is about 17" +/-. I'm a little baffled as to why the desktops weren't designed around that dimension, but rather went "really damn wide" even for a desktop. Adding a U of height would have made for a much more usable tabletop package as well, IMO. 6U is a perfectly acceptable size for a rackmount synth (the venerable OB-Mx is 6U and that's a wonderful rack interface, IMO, so there's no argument against it from a "it just doesn't work" perspective that I could find valid). They change the layout already (in the case of the P12 it's changed utterly) from the keyboard version, so trying to keep "some" compatibility can't be used as an excuse either.
I get that "rack mount synth" is a genre, but they didn't have to advertise them as rackable. They could still be sold with wooden end cheeks and just maybe an optional "one-size-fits all pair of rack ears" to go with them.
For their dimensions they don't work at all for me, though, and so I can confidently say that I'd rather buy the keyboard version, which inherently limits the number of DSI synths I will own, flat out. If they were rackable I could easily see adding another ... perhaps several, really.
You lose a ton of flexibility for transport and mounting and gain.... wasted desk space. I don't get it. Enlighten me, please?
(P.S. I am not looking for "here are ways to franken-pseudo-rack them"... the 19" rack standard is a standard and like it or not it's useful, human-scale, and ubiquitous. Standards are always procrustean beds, that's just how it is.)