Hello Tgmusicman;
Yes you can disconnect the HDR and boot the d8b on it's own.
You can also boot the HDR independently from the d8b.
There are plenty of people here on this forum who are willing a very able to help you with your questions.
It is all about describing your setup up (what and how you have things connected) then asking your question(s).
You can also search this forum by typing in your request in the "Search" field.
Welcome to the Forum and good luck
Bruce