For those DJs that also do club gigs (especially when the club uses Pioneer CDJs), it's also a plus to be able to practice on decks with just a USB stick with the song files.
For me, there are times when I just want to bust out the turntables and actually bring out the crates. Plug the turntables into the MCX8000, and you are ready to go-- since the MCX8000 is also a standalone mixer. Add the computer and control vinyl, and you can also have Serato on decks 3-4.
The MCX8000 is an attractive piece of kit. If I didn't have the DDJ-SZ, then I would consider this. The only gripe I have against it is the mirrored layout, but overall, this was a well-thought out unit.
I'm still holding out on an improved version of the SC3900 spinning platter-- one that doesn't need an extra USB cable per deck to use with Serato, and has useable color touchscreens for non-DVS/USB use!