Ok,
No luck so far on finding an electric trigger for the Spyder Xtra, I guess I'm going to actually have to ask Just Paintball if they can import it...
As for the trigger mod....I've switched my trigger frame from the Xtra as it was a bit worn, with a mate's mint but malfunctioning, Sonix, this left a bit more play in the trigger than the Xtra's frame, though they're pretty much identical and I thought I could use joebobs mod to get rid of the play and also get a more responsive trigger.
I got hold of some Fibre washers from an auto spares shop (very thin and compressable) and have fitted them under the grip frame and screwed the bolts in tight. The safety still locks the trigger, but when I take the safety off and move the trigger a millimetre, it releases the sear. Gives a more responsive trigger but wont cause the problems Joebob seems to be reporting!
So Fibre washers and a sonix gripframe seem to be the answer