Taro,
Yes, the DBX Driverack2 can be used for loudspeaker management from any era, including your 1970s/1980s speaker collection.
The manual explains the functions, like parametric EQs, limiting, and driver alignment delays on each output with independent crossover filter and frequency selection for each bandpass.
If you utilize all the features properly, you could improve the sound and output of the system compared to an analog crossover that does not have those features.
If not properly "dialed in", you could make the system sound far worse.
Best to tune the system outdoors to avoid room influence on response.
The two different types of 18" drivers and cabinets have different box tuning frequencies and frequency response, so could use different EQ and high pass filters.
The two different types of mids (ported, not ported) could use different EQ and time alignment at the low to mid crossover point to optimize response.
The two different high horns are probably more similar depending on drivers, "close, but no cigar" as they said at the carnival.
The proprietary AutoEQ™ is almost useless- usually results in a bizarre equalization that works in only one place in the room.
The subharmonic synthesis should also be avoided, don't need vocals sounding like Darth Vader and bass and kick adding more content below what the old 18"s can produce.
Have fun !
Art