Go Active Crossover or Upgrade existing XOs?

Anything is possible with money and time.  But then with too much money and time will lead to hubris.  And that's why God created men and women.  

OK, enough hubris from me.  

From your question it's obvious that you don't have the technical skills to start from scratch using any kind of active crossovers. To get it right is a complex process even for an experienced person, my recommendation is to leave it alone and save yourself time, money and frustration!

Give the guy a break, will you!  He may actually know more than you.

Digital cross-overs are unlimited, though stock cross-overs and firmware only touch on what is possible with advanced signal processing which can do things that no analog cross-over, active or passive could ever do, especially integrated in design with a purpose built amplifier.

Surely they have no side-affects?

With a digital input, only the side effects you intend, which any speaker is going to greatly swamp.

Hey, can I go with "DSP" and live happily ever after?  

Is asvjerry posting in Engles?  No comprendo muchachas.  Es poquito?

Talking about "DSP" engineering an cost ... as a saying goes "A good engineer can do for a penny for what a mediocre engineer can for a dollar."  But I don't do cliche.  Nobody has ever said that an "evil engineer will take the dollar and maybe even your soul".