Apple Remote Desktop, 2010 Mac Pro, and six displays

Question

Under 10.8, we were able to operate a 2010 Mac Pro (MacPro5,1) with 2 x HD5770 video cards and 6 x LED Cinema Displays (the mini DisplayPort models, two of them via IUSB-powered Atlona DVI Dual-Link-to-mDP adapters, via Apple Remote Desktop.
Under 10.9 (currently 10.9.2), all the displays still work, but ARD is having significant heartburn: if it is able to connect with the ARD agent on the display syste, the display arrangement is incorrect, and no amount of swapping mDP cables, moving the displays around in the Displays System Preference pane, and/or rebooting appears to help. Oh, and the most recent end state, when I finally managed to get the menu bar on one of the displays on the top (physical) row (we have them arranged 2 x 3, in order to display 4096 x 4096 pixel movies of spacecraft data), flummoxed ARD completely --- it simply refused to connect with the display machine at all. (I can ssh into the display system and use a cabled keyboard and mouse as well, but that's not a long-term solution: we have to be able to operate remotely, as we did under 10.8.) Oddly, ARD works OK, if not perfectly every time, with the target system when it's only connected to four or fewer displays (regardless of whether they're connected to mDP ports or via the Atlona devices). The host ARD system is another MacPro5,1 with 24 Gbyte of RAM; the target has 96 Gbyte.
Reading the release notes for ARD 3.7.2, it sounded as though all our issues would be addressed, but alas, it is not so: we're still stuck with ARD trying to but unable to open a "Control" connection to the display system.
Does anyone have any experience, positive or negative, with a similar setup under 10.9 and ARD 3.7.2?
Is there any way to clear all the settings in ARD? I can't find any .plist files with client system-by-system info in them, and I suspect they are (appropriately) encrypted because they can contain passwords, or at least store the hashed passwords in encrypted fields.
Thanks in advance for any clues for the clueless.

Answer 1

Mac Pro
Date introduced 
Original Mac OS X included
(see Tips 1 and 3)
Later Mac OS X included
(see Tip 1)
Mac OS X Build(s)
(see Tip 2)
Mac Pro (Mid 2012)
Jun 2012
10.7.3
10.8
11D2001, 12A269
Mac Pro (Mid 2010)
Aug 2010
10.6.4
10.7, 10.7.2, 10.7.3
10F2521, 10F2554, 11A511a, 11C74, 11D2001
Mac Pro with Mac OS X Server (Mid 2010)
Aug 2010
10.6.4
10.7, 10.7.2, 10.7.3 (Server)
10F2522, 11A511a, 11C74, 11D2001 (Server)
Mac Pro (Early 2009)
Mar 2009
10.5.6
10.6
9G3553, 10A432
Mac Pro (Early 2008)
Jan 2008
10.5.1
10.5.2, 10.5.4
9B2117, 9C2031, 9E25
Mac Pro
Aug 2006
10.4.7
10.4.8, 10.4.9, 10.4.10, 10.5
8K1079, 8N1430, 8N1250, 8K1124, 8P4037, 8R3032, 8R3041, 9A581, 9A3129
I expect your Hardware is essentially unchanged since the 2010 model, and should run the custom 10.6.4 they provided, or 10.6.5.
The "Full Retail" 10.6.3 is only 10D575, so it will not suffice.