Practice and Theory are two different things unfortunatley in this hobby.
Fact is yes 400 watts output helps, it will control the speaker better, and maybe give you a useable boost of 3 db from say a 200 watt amp. Or 6 db over a 100 watt amp as you will be forced to turn it up more (using passive).
A 89 db load is not bad, but trust me when I tell you this the entire "Gain Chain" from efficiency of the speaker to the true voltage output of devices creating the proper overall gain is necessary to make a Recording sound like it should. Not so much Passive vs. Active.
The best way I can point you in true USEAGE vs. Theory is this :
A more Sensitive amp input (nothing to do with impedance) with better gain will help to play most recordings that need help over Amp output power vs. speaker sensitivity.
In otherwords going passive from many experiments in my testing is that you want an amplifier that will go to FULL power with about 1.5 volts or less. And have a gain of at least 28 db in general.
The example I gave above with the Mcintosh amp in theory was exactly what I am talking about. That AMP took 4.5 VOLTS to push it to its full power quite a bit over others, that means even with most XLR sources thru a passive we might get about 4.0 volts start to stop. Not only that it had about a 20,000 ohm input impedance if I remember right?
Anyway it also had 24 db of gain.
It was good, but lets put it this way if you want the dynamics and capability of full blown "Metallica" rock or some other stuff believe it or not a "High Gain" input amp with lets say 30 db vs. the 24 db in this case is far more effective than 400 watts or 100 watts feeding a 89 db speaker.
Both amps have enough output to rock the house with that speaker. Problem is the "Gain chain" in front of it that if not handled right in the first place can dissapoint and sound flat.
In theory for a passive any amp with less than 2 volts necessary to drive it with an input impedance of 100,000 ohm should ideally work fine in a passive situation, but this will not guarantee you will like it.
By the way another reason I mentioned the McCormack amp as an example... It only took 0.8 volts to drive full power, and has a 100,000 ohm impedance, and had 31 db of gain
all around perfect to test a passives true capability as it almost had the 6 db active preamp built in. There are other amps I used like this such as Clayton mono blocks that have 29 db input gain and 100 k impedance as well, but very expensive.
Some amps will work, but you still may end up short if you are use to having that EXTRA power at the top end you get with Active preamps unless you really have the right amp. Even some tubes can do this well and only put out 20 to 100 watts. You really need to know how much voltage to drive that amp it really takes, and gain helps.
As stated above you can always try one first if you have a way to do it. But if you don't like having your volume 50% to 80% all the way up a lot of the time it might not work out well with your current speaker and amp combo even if that amp was 1000 watts.
