Ok, I misunderstood your intent then.  I think I got that impression from you mentioning using the Multiface as an external A/D D/A with the HDSP9652.
 

I thought I recalled somewhere a capability to daisy-chain multiface units, but taking a look at the unit itself I only see a single host port, so I believe that I was wrong in that regards.  In which case it limits the possibilities of cards playing well.

It is, of course, a bit more tricky to combine the three cards into a single unit for use with Jack if there are three separate cards.  I believe it is possible to have three multifaces, with three interface cards, so long as they are properly syncd via wordclock it should work in theory.  However note that I have never tried it, it is a more complex setup, and personally I think I would lean away from it in favor of doing a single interface that has plenty of I/O for what you need (Like your original thought with the 9652) and external AD/DA (Which RME has some units dedicated to this purpose along with the obvious choices like Apogee).
 

If memory serves, the HD24XR IS the HD24 with a bit more processing.  It is only capable of 12 tracks at 24/96 I believe though, not the full 24.  In my experience with the HD24, I find them to be a good machine for recording live shows, however transferring the show off the HD24 I found it to be a much better solution to use an external USB enclosure, and use third party tools to transfer the information directly from the drive to my local drive.  I can look up the program I used if you would like. 

Their FTP server I consider to be complete crap for transferring recordings of any length over a couple minutes.  Doing 1 hour recordings and above, it continually crapped out on me in transfers and was extremely slow on top of that.  Compared to the direct connection method mentioned above, which was far more stable, far faster, and in general far better, I would never touch their FTP transfer again.

I have not used their fireport transfer method though I have heard it is decent.  It sounds like you were looking at transferring by wiring ADAT and recording in real time form the playback of the HD24?  I would say, especially when using Ardour, it is better to transfer the files via direct connection as mentioned above, but this is just personal opinion.  In dealing with largee track counts of large shows, it is probably a moot point so long as you never have a problem doing the recording in Ardour.
 

Ok just tossing it out there, personal preference only;)

       Seablade