Have you try'd out the djm 2000 mk1? It is essentially the same as the 2000 nexus except for the new beat slicer and master tempo syncing. If you have not tried either the 900 nexus or 2000 mk1 or the new 2000 nexus I suggest you go to a place like Guitar Center where you would be able to see for your self. As far as my opinion I say if price is not of importants go with the djm 2000 nexus, if price is an issue than I say the 900 nexus.
If you where to purchase the djm 2000 nexus you have pretty much all the beat effects on the 900 nexus except for the spiral and melodic which to be honest the only one you are going to miss is the spiral which is a awesome effect, melodic was a failed attempt trust me. As far as color effects and or instant effects if you where to go with the djm 2000 nexus you would be missing the space effect and dub echo which is on the 900. These effects especially the space color effect is awesome to use when needing another option to take the place of echo. Now vise versa if you where to get the 900 nexus you won't be able to use the new beatslicer or use the frequency mix option. Also the djm 2000 nexus effects allow the user to use the beat effects and only effect certain parts of the track for instance if you only want the highs effected this mixer would allow this or just the mids or lows only ect.. While the 900 nexus is a great mixer I purchased it because I got a great deal on it. Such a good deal that the few extra features the original djm 2000 had to offer did not justify the price jump. So if money is not an option go with the 2000 nexus you will only miss the space, spiral and x pad is such a great feature. But if you want to save your self a few hundred dollars you won't really miss what the djm 2000 nexus has to offer over the djm 900. Regardless I do recommend you try it out yourself if you can.