If using 16992 provision, the login account/password of WEBUI will be admin/P@ssw0rd.
But I'm wondering if I'm using 16993 provision, where can modify WEBUI account/password? ACS in SCS console? or ??????
Regarding your question, Where to modify the username and password when using 16993.
According to the manual
You should be able to manage the username and password at the NetworkSettings.xml.
I will check futher on this to see if I can find a better answer for you.
If there is anything else we can help please feel free to ask.
The access to WebUI should have no problem using AMT after 6.0.
Port 16993 is the correct port to use if you have enabled TLS in their profile (see section 5.10 of the SCS User Guide or section 4.10 of the AMT Configuration Utility User Guide). If TLS is not enabled, then you have to use 16992.