Audio devices in the system :
1. ) Built-In Analog I/O (2 ch each In & Out)
2.) Built-IN Digital Audio 2 ch In
3.) SSL MadiXtreme (64 ch each In & Out)
4.) Digidesign MBox original version with Digi driver (2 ch each in & Out)

Standard Input / Output set in System Preferences
All tests done with coreaudio driver

Test 1 : Self created aggregate device  
Devices 1,2, 3
Standard Input & Output  : aggregate device
Ardour In & Out                  : aggregate device 
 
Get message : Could not reconnect to the Audio Midi engine - BUG ?

Test 2 : Self created aggregate device 
Devices 1,2 (left out digital in)
Standard Input & Output  : aggregate device
Ardour In & Out                  : aggregate device 
 
Opens fine
Ardour sees : 66 ch each Sources & Destinations

Test 3 : Self created aggregate device 
Devices 1,2 (left out digital in)
Standard Input & Output  : Built-In Audio
Ardour In & Out                  : aggregate device 
 
Opens fine
Ardour sees : 66 ch each Sources & Destinations

Test 4 : Self created aggregate device 
Devices 1,2 (left out digital in)
Standard Input                   : Built-In Audio
Standard Onput                 : aggregate device
Ardour In & Out                  : aggregate device 
 
Opens fine
Ardour sees : 66 ch each Sources & Destinations

Test 5 : Ardour hidden aggregate device ???
Standard Input & Output  : Built-In Audio
Ardour In & Out                  : Built-In Audio 
 
Opens fine
Ardour sees : 2 ch each Sources & Destinations

Test 6 : Ardour hidden aggregate device ???
Standard Input & Output  : Built-In Audio
Ardour In & Out                  : aggregate device 
 
Opens fine
Ardour sees : 66 ch Sources & Destinations

Test 7 : Ardour different devices
Standard Input & Output  : Built-In Audio
Ardour In                             : Built-In Audio 
Ardour Out                          : aggregate device
 
Opens fine
Ardour sees : 66 ch each Sources & Destinations  -- BUG ?

Test 8 : Ardour different devices
Standard Input & Output  : Built-In Audio
Ardour In                             : aggregate device
Ardour Out                          : Built-In Audio
 
Opens fine
Ardour sees : 66 ch each Sources & Destinations  -- BUG ?

Test 9 : Ardour different devices
Standard Input & Output  : Built-In Audio
Ardour In                             : Built-In Audio (digital)
Ardour Out                          : Built-In Audio (analog)
 
Get message : Could not reconnect to the Audio Midi engine - BUG ?

Test 10 : Digidesign MBox test (original version)
MBox doesn't show in system preferences but in Ardour (no digi driver open)
Standard Input & Output  : Built-In Audio
Ardour In                             : Digidesign MBox
Ardour Out                          : Digidesign MBox
 
Opens fine
Ardour sees : 2 ch each Sources & Destinations (wow - didn't expect that)

Test 11 : Digidesign MBox test (original version)
MBox doesn't show in system preferences but in Ardour
 - digi core audio manager loaded
Standard Input & Output  : Built-In Audio
Ardour In                             : Digidesign MBox
Ardour Out                          : Digidesign MBox
 
Opens fine
Ardour sees : 2 ch each Sources & Destinationst (this time, I expected that)

Test 12 : Different devices including MadiXtreme / MBox
MBox doesn't show in system preferences but in Ardour (no digi driver open)
Standard Input & Output  : Built-In Audio
Ardour In                             : MadiXtreme
Ardour Out                          : Digidesign MBox
 
Opens fine
Ardour sees : 66 ch each Sources & Destinations  -- BUG ?

Test 13 : Different devices including MadiXtreme / MBox
MBox doesn't show in system preferences but in Ardour (no digi driver open)
Standard Input & Output  : Built-In Audio
Ardour In                             : Digidesign MBox
Ardour Out                          : MadiXtreme

Opens fine
Ardour sees : 66 ch each Sources & Destinations  -- BUG ?

Test 14 : Different devices including Built-In Audio / MBox
MBox doesn't show in system preferences but in Ardour (no digi driver open)
Standard Input & Output  : Built-In Audio
Ardour In                             : Digidesign MBox
Ardour Out                          : Built-In Audio

Opens fine
Ardour sees : 4 ch each Sources & Destinations  -- BUG or feature ?

Test 15 : Diff devices incl. Self created aggregate device / Built-In  
Devices (aggregated) 1,2 (left out digital in)
Standard Input & Output  : Built-In Audio
Ardour In                             : aggregate device
Ardour Out                          : Built-In Audio
 
Opens fine
Ardour sees : 68 ch each Sources & Destinations  -- BUG ?

Test 16 : Diff devices incl. Self created aggregate device / Built-In  
Devices (aggregated) 1,2 (left out digital in)
Standard Input & Output  : Built-In Audio
Ardour In                             : Built-In Audio
Ardour Out                          : aggregate device
 
Opens fine
Ardour sees : 68 ch each Sources & Destinations  -- BUG ?