It seems that people have devised their own work-arounds for multi-quoting. There is an easier (and dare I say correct?) way to do it.
TR72, if you want to quote several posters in one of your post, then all you need to do is click on the button with the quote marks within each post you would like to quote. It is the multi-quote button and will turn red.
As you scroll down the thread and click on that button, they will all turn red which means they've been selected. In the image below, you can see that the first, third, and fourth buttons are red, but the second is not:
Then just click on the regular old Reply button down at the bottom. All your selected posts will appear in the new message window in the order you clicked on them.
The end of each quote is delineated by the "end quote" code (straight brackets around a forward slash in front of the word QUOTE). If you want to insert comments in between different quotes, the way should be clear enough - just write in between each endquote and the beginning of the next quote.
If you want to split up one persons quote into a few parts and insert comments inside it, copy the beginning quote code that contains the username and post number inside the straight brackets. Then, you can delete text, insert your own and paste that code in front of that person's next paragraph you wish to include. Be sure to add an endquote to the end of first part where you broke up the text, before you insert your comment.
Doing that would look like this (the number signs stand for, well, numbers - the post's ID # to be exact):