I have merged all the multi CD albums on my B2 it is a simple to do if you have the NAS set up so you can access the music directory from your PC or Mac.
The folder structure is (using The Wall as an example)
Pink Floyd
02 Track 2
03 Track 3 etc.
The Wall CD 2
01 Track 1
03 Track 3 etc.
What I have done for multi CD albums is first to rename the tracks putting an extra number at the start of the filename. You can do this using Windows Explorer.
Pink Floyd
The Wall CD 1
101 Track 1
102 Track 2
103 Track 3 etc.
The Wall CD 2
201 Track 1
202 Track 2
I then copy the files from The CD 2 folder to the CD 1 folder
Pink Floyd
The Wall CD 1
101 Track 1
102 Track 2
103 Track 3 etc.
201 Track 1
202 Track 2
203 Track 3 etc.
The Wall CD 2
Finally I delete the now empty CD 2 folder and rename the combined folder
Pink Floyd
The Wall CD 1+2
101 Track 1
102 Track 2
103 Track 3 etc.
201 Track 1
202 Track 2
203 Track 3 etc.
The advantage of adding the extra number is you know, when looking at the track, what CD it comes off.
Hope this helps.
---------------------------------------------------------------------------------------