I have a huge number of songs and do djaying for diverse audiences. I would like to create and open different catalogues rather than the entire library.

I complete agree with this request. It would be invaluable for to have multiple catalogues. I tried messing with the file called:
C:\Documents and Settings\MYusername\Application Data\MixMeister Technology\MixMeister Engine Express 6\catalog.mdb. For a while it seemed that swapping this file into and out of its folder allowed me to manage different catalogues. However, after a short while this practice corrupted MixMeister Express 6 and I had to reinstall.

For the developers it should be fairly easy to implement a "Save Catalog as" and "Load Catalog" function.

Also, when I change certain mp3 tag information in the MixMeister Express 6 Catalog, other tag managers don't seem to see these changes. In particular, I would like to rate songs in Mixmeister and see the rating in other tag managers.

Other than that, I am deliriously happy with the product

I think what you want is the "Categories" feature that's in Studio & Pro. This allows you to assign songs to one or more categories, and then only display categories when you need them.

((( ardent )))