How can I merge double CDs, boxsets, and bonus material down to one grouping in iTunes?

By far the most annoying thing about iTunes to me is that it will separate double albums and songs that have bonus tracks onto two or more albums. I don’t understand why iTunes does this. The reason that some albums are released as double albums is that the albums were too long to fit on a single cd. Of course when using iTunes we don’t have that space restriction so why can’t I just merge everything together?

I have tried changing the title of the albums but that mixes the songs together oddly. It will play track one of disc one and then it will play track one of disc two! Obviously that wasn’t what I intended for it to do. What I find even more frustrating then splitting by double albums is that if you buy the disc and then buy bonus material on the albums from iTunes and Amazon you will have the bonus material just group by where you purchased it. One of the albums I have lists the album three times because both iTunes and Amazon had bonus material that I got from that album that could only be bought at certain stores. How can I get them all merged together into one album?