The spark was the capacitors charging. BNIB amps, or ones that have been sitting disconnected for extended periods of time can be slow bled a charge for their capacitors with a trickle charger to avoid this. In 99.9% of the cases, the spark does nothing, in the .1%, the amp fries. When I connected my first power to my Warhorse, I thought I blew a hole in my bed. Thing sounded like a gunshot. I just knew the amp was fried (as I have heard plenty of KX1200.1 and ZX1500.1 pop and they weren't near as violent). Amp was just fine, it just has eleventy bajillion huge caps that needed to fill.
As previously stated, check your remote and/or any connections for looseness. Also check in-line fuse on power wire if there is one. When you heard the large pop, you may have fried that fuse. Never know.