It's well worth the exercise learning to solder. I'm no expert, but I get by. A thin tipped temperature controlled station is well worth purchasing. I prefer a hot tip with a minimum contact time. Just enough to get the solder flowing with a nice silver surface when cooled. The cheap ones on eBay seem ok for occasional soldering. A thin roll of solder with resin is also good.
In my own case, there wasn't a schematic as I upgraded the components in my existing crossover. I followed the path on the circuit board and created my own.
Good luck and it's not that difficult.
