We use all Zeiss medium format glass, and various bodies to make use of them:
Sinar m - for multishot, repro, and high speed AF
Contax 645 - zoom lens, TTL flash, and backup for m camera
Hasselblad 201F - leaf shutter/high speed flash
Hasselblad Flexbody - modified for additional front tilt/shift , portable technical camera
Hasselblad 903SWC - repro, some landscape
We had the Hy6 system as well, but recently sold it in favor of the Sinar M system. The Hy6 is a wonderful camera, but we found the M to better meet our needs for the various Zeiss glass that we prefer. The Sinar m can also be used as an electronic shutter for the Sinar p2/p3 cameras. In addition, it can also be used as a unique rangefinder with the Rodenstock HR28mm lens (unique since it uses an electronic focal plane shutter capable of 1/2000, and also supports multishot without a Rollei shutter/control unit). This system is well integrated, as the Hasselblad V glass can be used interchangeably among the camera bodies. Of course, the FE glass can only be used on the Contax, 201F and M cameras.
We only use two types of digital backs for all of the above cameras:
Sinar eMotion 75LVII - with Sinar m, Hasselblad V, and Contax 645 adapters
Sinar 54H - also with Sinar m, Hasselblad V, and Contax 645 adapters
David