Reply to Stuck between S4 or mixer + x1

Please can someone tell me an advantage or disadvantage of buying a s4 over a setup of a 4 CHANNEL mixer and an x1 (+sound card)?

I dj at party's a lot but most of my djing is done in the studio.

The S4 is getting old now and just wondered whether it would be better to buy a mixer and x1 over a s4 or the other way round?