Agreed, if you are using active crossover, especially with two different types of amps, you really need to get actual speaker response measurements. This does become more difficult in your own home, unless you build some sort of sound absorbing tunnel (or do something outside aiming the speaker up with an infinite baffle type of area. You’ll need some sort of gain adjustment if you use different amps, or you will have to put in some sort of level adjustment in the passive crossover. Generally, people who bi-amp will use the exact same amp for highs/lows, but it may be a waste of expense to buy a second Modwright amp. I guess the pro audio amps are good because they do come with a gain adjustment.
You could change to a QSC amp if you wanted to if you look for a Class A/AB. Pro audio amplifiers are designed to work in extreme environments, push a lot of -general- power to speakers that are extremely efficient (i.e. 98db/watt) and be as efficient with the A/C power as possible. Hence, more Class D/H/I style amps with switching power supplies and fans. What you want is more of a linear power supply with huge amounts of power supply capacitance and lots of output transistor devices. Usually, this does mean looking for an amp that has a lot more watts (since you need that bigger power supply to be able to push the watts), but it does not mean you have to use all the power. It just means that you have enough brute force from the power supply to drive speakers with low or radical impedance curves.
I have used a Crown CTS600 and a Crown CTS2000. The CTS 600 was a Class AB amp. The sound quality was okay, but somewhat dry. The CTS2000 was definitely stronger and better for woofers, but it was a Class I (Class D variation) and it definitely had some tube-like overtones/colorations in the sound. The Emotiva XPA-1 monoblock was significantly better than either of these Crown amps. Emotiva was totally stronger than either and just sounded better overall. Much more current on tap.
As far as I remember, a Zobel will not change the basic impedance of the speaker. It will still be 4 ohms. A Zobel is to control the rising impedence as the woofer tracks towards the higher frequencies. It’s good to put in a Zobel for the woofer anyways. See this:
https://trueaudio.com/st_zobel.htm
The Modwright is an excellent amp. My suggestions of the Emotiva XPA-1/1L and the Parasound A21 was to try to get a good enough amp to match the resolution/fidelity of the Modwright for the lower woofer registers. You don’t have to spend as much if you don’t want to. You could even go with a single Emotiva XPA-2 (2 channel), or other alternative. In the end, you get what you pay for. Actually, the Parasound A21 has a gain adjustment on the back, so it may work well unless the internal gain of the Modwright is so much higher.
