For DIYs, Id consider adding active crossovers as a permanent test component. Testing various XO points with passive units can be time-consuming and expensive. Active XOs are ideal to quickly dial-in and sound test different crossover points. Some offer 2-3 way stereo in addition to 4-5 way mono.
For a 2-way cabinet, knowing the recommended lowest crossover point for the drivers is critical to prevent damage. For example, if your tweeters are recommended at a safe 2500 Hz minimum XO, and a smaller bass driver plays relatively flat up to 5-8 kHz, you can safely dial in different XO points at 2500, 4K, 5K, 6.3K and 8K. Simply listen to different XO points to determine the best sounding XO point for the two drivers musically while playing your favorite musical or test tracks.
If youre unfamiliar with active crossovers, the processors L/R analog outs go to the L/R active crossover inputs. The active crossovers spilt your processors single outputs into two outputs for connection to separate amps for the bass and tweeter sections. A 2-way cabinet requires two amp channels per cabinet, a 3-way requires 3 amp channels per cabinet, etc.
One method is looking at the spec sheets on your drivers. Look for the flattest frequency responses and matching sensitivity ratings of each driver. Example: If 8 ohm 95 dB sensitivity bass drivers play flat from 60 to 6K, and 8 ohm 95 dB sensitivity tweeters play flat from 2.5 kHz to 16kHz, the best level control for both drivers is a likely a XO between 2500 to 6000Hz.
Once the best XO point is determined using active XOs, buy separate quality passive crossovers and return to single amp channels per cabinet. Alternately, keep the active crossovers and separate amps for each driver. When going fully active XOs, many recommend extra protection for the tweets in case of a upstream component pop while switching sources or when turning components On/Off.
A passive, inline 2000-2500 Hz high pass capacitor will protect the tweeters from any sudden spikes from the dedicated amps. Active XOs often use 4th order Linkz Riley (spelling) filters, too, and well-regarded by many.
Parts Express, Madison Sound, and Meniscus are good online sources for DIY ideas and tech support.