Christmas Episodes have always had, ...let's say a different build of new theme, remember Series 4 with the Voyage of the Damned? that was the first time we got a new remixed Intro, and that one had a MUCH louder drum mix compared to the final one we got for the rest of Series 4.
Here I consider it the same thing, The Snowmen mix felt very chaotic and had cold highs, where as the one we have now feels more toned down so everything is in line, yes the sparks have been turned down to, and the bass and synth of the main theme have been raised so they are more clear.