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Not exactly -- if you don't have an SL box, mixer which supports the Club Pack or a controller that unlocks the software, you can't just use Serato. Serato DJ has specific requirements as to its audio interfaces and if you're not using one of them, you can't use the software even if you pay for a license.
If you are using a DDJ-SZ and want to use your XDJ-1000's, that's fine because the SZ unlocks Serato DJ, but if you have a DJM-800 and XDJ-1000's, it won't work simply because you previously used a DDJ-SZ; the DJM-800 isn't capable of supporting Serato DJ's audio requirements even if the XDJ-1000's can control the software.