To be clear it isn't possible to add files to the VirtualCD (and have them associated with the original disc) for files already on your PC.

If you just need to know what disc an Album is associated with you can keep using the Custom field route and not scan the CD's in MediaMonkey. The only benefit you derive is that when you insert the disc MediaMonkey knows that files on your PC belong to the inserted disc (something you already can see from the Custom field).

I have lots of CDs and all have been copied to flac. Every CD has been given a number like A001, A002 etc which I placed "custom 1" field. So there are 2 entries for each song in MM. I want to be able to play the flac on my pc and also know where to locate the original physical CD by looking at the "custom 1" field.

I was trying to make it only one entry for each song in MM. Dont I have to combine the 2 entries using Virtual CD to achieve this? Is there an easier way?

It can only be done with MediaMonkey directly from CD. Any reason you want to use VirtualCD?

I have a few hundred CDs that I created flac copies of before finding out about MM. I used EAC to do it. With MM Gold, can I create Virtual CDs with the existing flacs, or do I have to create flac files all over again with MM? If I follow the help guidelines, it looks like I have to re-do the flac files.