I had the opportunity to try and compare side by side the XL and the Synapse Bass guitar through 2 different amplifiers -Fender and Peavey- and frankly i did not notice big differences, in fact, Synapse could match the tone of the XL and bigger, but not the other way. The Synapse has more posibilities.
Something similar happened when i compare a 197??? P bass with my 2011, American Standard, mine sounded better in my ears and in the opinion of 4 guys who were there.