yeah, specs may be more important with subwoofers where you want to design your own subbox and know what fits and works.
most splits are 4ohm impedence, so consider what power your amp produces driving 4ohm loads to determine if the amp will be suitable (usually is).
enclosures are far less critical for splits if you mount the woofers in the doors. midrange driver and tweets usually require nothing special here.
therefore, as RTTZ says, your auditioning opinion is what's important. and when you do audition, play music you're familiar with, audition as many as you can, cheap and expensive, and note what amp they're being driven by (try and have them driven by an amp similar in quality and power to your own).
if you do want to know about specs and how they relate to subs, then...it's complex and mostly beyond me! but we can answer that as necessary.