Also check out the Vestax TR1
For portability, I think I would take a X1 (or 2 for more versatility). In combination with a club mixer awesome (even though for that usage the Dn-SC2000 is even more awesome imo), but more than capable of being used all on its own (just remap the FX section to 3-band-EQ and volume knob).
Faderfox 4midiloop?
On topic: i just use my x1 and a2 soundcard, but if your looking for more fun i guess you could use the vci100 and somehow map sample deck usage into it 
That thing is so so so expensive.
He asked for a 4 channel midi mixer 
just saying that, what about the ddm4k ?
love that the 4midiloop is considered off topic 
Seriously who is that thing aimed at?