The name 'Houdini' was Apple's internal code name for the original Apple DOS card. In this FAQ, 'Houdini II' and 'DOS card' will be used interchangeably to refer to the Apple DOS Compatibility Card for the PowerMac 6100. This time it is Houdini with a bigger budget and in more flavors. Bigger budget means that the Houdini II will include more features. The Houdini IIs also include SoundBlaster support.
More flavors refers to the different kinds of Houdinis available.
The Reply Co. DOS card is basically an enhanced version of the old Houdini I card. Reply has just licensed the technology from Apple. The connector on the original Houdini card was for purpoese of testing and debug. It will not support the inclusion of a Sound Blaster card. The connector on the 6100 DOS card, though looking similar, is different and not compatible.