I recently acquired a pair of X3's and first and foremost I'd call them revealing with an omnipresent quality. I've tried five amps with them, leading the pack is a Naim Uniti Nova. The combination has quick reflexes and an exquisitely controlled, musical, extended bass. I only have two memories of systems I'll never forget and the X3's belong right there with them.
I know that many of the AC guys love tubes with Spatial speakers but I'm interested to know what else folks have successfully paired with their Spatials. The Nova is my favorite out of Hegel H390, Vinnie Rossi LIO with VR120 or Musical Fidelity 550K Superchargers and my plucky Naim Nait 2.