you should really try out swinsian, it is sweet, fast and worth every 24$ penny.
to sync your playlists from swinsian to traktor/serato, you have 2 options i can think of:

* there is tool called 'ximian' which generates an itunes library xml file from your swinsian playlists. note that it will overwrite your itunes library xml file, so make sure you back that first. after downloading, open a terminal and run:
chmod +x Ximian
and it generates an itunes xml file from swinsian. if this works, then you can stop reading here and enjoy itunes playlist integration in traktor/serato.

* now, i didn't get ximian to properly export my swinsian playlists (but it exported _all_ my tracks from swinsian to the xml file). so instead of relying on the itunes xml integration in traktor, i use a custom apple script which syncs all files from a swinsian playlist called "trax" into a new folder on my computer. this folder is the same folder i read files from in traktor. this should work similarly with serato. now i have 2 copies of some tracks for dj-ing, but this way i can enjoy making playlists in swinsian, without manually adding/deleting files in finder.

this is the script, which you can run with
osascript swins2trax.applescript
in your terminal or easily add to an macos automator:

-- copies all tracks from the playlist "trax" in swinsian to a directory

set thelist to "trax" -- name of swinsian playlist, change if desired
set thedest to "/Volumes/space/Trax/" -- destination directory, change if desired
set thedesttmp to "/Volumes/space/.Trax/" -- this gets deleted after syncing
	do shell script "([ -d " & thedest & " ]); exit $?"
on error
	display dialog "Error: directory " & thedest & " is missing"
	error number -128
end try

tell application "Swinsian"
	repeat with theplaylist in playlists
		set thelistname to name of theplaylist as string
		if thelistname is equal to thelist then
			do shell script "rm -rf " & thedesttmp
			do shell script "mkdir " & thedesttmp
			repeat with thetrack in tracks of theplaylist
				set thefile to location of thetrack
				do shell script "cp -a \"" & thefile & "\" " & thedesttmp
			end repeat
			do shell script "rsync -auvv --delete " & thedesttmp & " " & thedest
			do shell script "rm -rf " & thedesttmp
		end if
	end repeat
end tell

display notification "All trax are ready!"
link to script file: