They're both versatile; and each is more versatile than the other in specific ways -which are obvious (Signature controls have INDIVIDUAL filters AND Qs for each pickup -individual/separate tone control- and Europa electronics have the benefit the bass and treble switches -which multiply your tone variations by 9.)
But it would be a simpler and cheaper upgrade to add the 2 switches than to switch to Signature -I'm pretty sure.
I'll tell ya from experience, the ULTIMATE is having BOTH a filter with a variable Q AND bass & treble & mid-range controls for EACH pickup -with the option to assign EITHER pickups tone controls as MASTER tone controls for BOTH pickups... this gives the best of both worlds!
Working from the premise that you must choose between EITHER the Signature controls OR the Europa controls... well, you can't go wrong with either choice; and each has it's pro and it's con... it's really Yin & Yang. Really.
Just remember, you can step outside the box. You can step outside the lines. You don't HAVE to choose between the two... you CAN, in fact, choose to have BOTH. If and when you do, I'll just tell you, it works!!!
I think the best bet might be if they can just send the switches with instructions, and have your genius tech guy work some magic.
But if you DO send it back to them for the upgrade, I STRONGLY recommend also BOTH upgrading the Q switch to 3 positions AND also adding a MID-RANGE boost/cut switch. Having bass, mid, treble, and variable Q control features allows awesome control over your sound. And educate yourself about the brass sustain block. If you don't know about it, ask around. My Elan doesn't have one -I don't think it was standard on them. If you play an Alembic that (all things being equal) DOES have the sustain block, you'll notice the difference. If you do send it back, it would be an opportunity to address that, and increase your sustain.
Best wishes
