Hi mamat
I own a nord 2 rack and can honestly say that it is one of the best pieces of kit that I have ever bought. The range of timbres that you can get is quite remarkable from nice round Juno style basses, to tight percussive Oberheim SEM type snaps and squarks. I have also compared with many other virtual analogs (JP8000,AN1X,Z1,) and it is much tighter than the others, although the roland has nicer pads (FX probably) neither it or the others come as close as the Nord at replicating the sounds of old synthesizers. The machine is splitable, 4 ways, and these can be assigned different MIDI channels and/or note ranges. The arppegiators are independent to each sound.
I have recently tried the Nord modular and although it is a very powerful and good sounding machine, the reliance on having a PC in tow to do any serious editing, unfortunatly make it less immediate, and the machine I tried had a number of bugs which were rather frustrating.
I hope this has been of some help to you

simon