The only way to group these entries into a single item is by changing titles. The general rule for multiple-disc albums is as follows:

If several albums have identical artists, titles, formats and are properly numbered (for example: 1/3, 2/3 and 3/3), they will be recognized by OrangeCD as belonging to a set.

So, you need to make sure that artist and title are the same for all items (format will already be the same as you added them from one source), and re-number them manually.

I hope this helps.

Andrei