Good point, I used the VGA adapter to be adapted to my 27" iMac -VGA to Thunderbolt.
Coming out of the PC monitor.
First problem fixed, got the 3 monitors accomplished!
I really do appreciate you Luis for responding!
I finally fixed the problem with the help of an tech support guy from AppleCare .
When I finally lined up the two iMacs and the PC monitors. What I didn't do was to press the Command key and the F2 key together on my second IMac monitor which is the "Target" monitor which is the slave to the main 27" monitor.
Then and only then did I see the 3 arrangement windows show up form the Preferences - Display section Where there was two, now there was finally 3. So I have to keep remembering that precious "Command +F2" key! in the "Target "iMac 21!
2nd problem not fixed:
Now that I have 3 monitors up and running (as long as I don't forget the process)
I have now my two thunderbolt ports filled up in my Master iMac 27" because of
the need to use them for the 3 monitors (Two iMacs +Pc monitor)
So being that I use Logic Pro X for composing, i use a UAD Audio Interface Thunderbolt!
That interface gives me high quality sound. But I have NO port in which to plug it into.
The Thunderbolt ports or "Mini Display Ports" are filled up. I went to Best Buy because Apple
store couldn't find what I was looking for, Best Buy could't find it either, a male (Thunderbolt to USB adapter)
so I could plug the Thunderbolt audio interface into one of the 4 ports in the back of my 27" iMac !
So I am at a brick wall. To my knowledge there is not a "Thunderbolt to USB adapter made". And not sure it would work either ! Because I want to have 3 monitors for all the windows I open up working in Logic Pro x.
I paid a decent amount of money for that Thunderbolt UAD audio interface and I just don't want to go out and by another. So many I'm stuck with two monitors working with Logic Pro X.
So I will send Universal Audio message asking them if there is a work around. I am not sure if they are discontinuing
the Thunderbolt model ! They do have a USB version which would be good but I just don't want to keep dishing out money buying audio interfaces!
Thanks again Luis for getting back to me !