Many years ago I helped someone in Madagascar get a pair of MMGs. The MMGs were only available direct from Magnepan, and Magnepan wouldn't ship to Madagascar, so I bought them from Magnepan and then shipped them on to Madagascar.
Imo in a large room, you want speakers that do two things well. The first is, "power response". The power response is the summed omnidirectional frequency response of the speaker system, so it includes all of the off-axis response. In a large room, unless you listen from very close to the speakers, by far most of the sound that reaches your ears will be reverberant field energy, and it is the power response that determines the spectral balance of the reverberant field. It just so happens that Maggies do an exceptionally good job in the reverberant field/power response department. You will be hard pressed to find a $2k-$3k box speaker that does as well, but it's not impossible.
By way of example, imo the wrong type of speaker for your room would be a something like a 6" woofer + 1" dome tweeter. The problem arises at the bottom end of the tweeter's range, in and just above the crossover region. The woofer's pattern will have narrowed due to "beaming", but the tweeter's pattern wants to be 360 degrees because it is so small in relation to the wavelengths. The baffle confines the pattern to 180 degrees, but that's still much wider than the woofer's pattern. So in the 2-4 kHz region or thereabouts (depending on exactly where the crossover is), you have a LOT more off-axis energy compared to most of the rest of the spectrum. And this happens to be right smack where the ear is most sensitive. So in a big room, where the reverberant energy is considerably stronger than the direct sound, you hear brightness and perhaps even harshness due to the tweeter's excess off-axis energy in that critical lower treble region. So beware of designs that have a big difference in cone/dome sizes, as you cannot have smooth on-axis and smooth off-axis sound at the same time from such a system, and in your big room, that really matters.
The key to good power response is good radiation pattern uniformity. There's more ways than one to get there, so for now, let's look at the other requirement because that will guide us towards the best approach to radiation pattern control for this application.
The other thing you need, obviously, is sufficient sound pressure level capability. Your 125 watt amp is a good start, but as you discovered, your sweet-sounding Maggies just aren't efficient enough.
Unfortunately high efficiency + deep bass = large box, and (usually) a high price tag. BUT, you have that problem solved already! Your pair of SVS subs frees you up to pursue high efficiency satellite speakers that have good radiation pattern control.
By the way, kudos for getting two subs instead of just one bigger sub. That greatly improves the in-room smoothness in the bass region. I manufacture a four-piece subwoofer system called the Swarm, but in a big room like yours, two subs is probably all you need for smooth response through the modal region.
Over in the prosound world, they long ago figured out how to do high efficiency and good radiation pattern control. Where the high-end audio world can improve on that is, sound quality. We can do a speaker that uses carefully selected prosound drivers and techniques to get good efficiency and good pattern control, and give it the high-end treatment in the crossover. Prosound woofers often don't go low enough for high-end home audio, but your pair of SVS subs makes that a non-issue.
The design approach I would take for a room like yours is, to use a fairly large-diameter high quality prosound midbass driver and cross it over to a 90-degree-pattern constant-directivity low-coloration horn at the frequency where the woofer's radiation pattern has narrowed to 90 degrees. I'm not the only one embracing this paradigm; I learned it from Earl Geddes (GedLee) and Wayne Parham (PiSpeakers), and JBL did it in their classic Model 4430 studio monitor 35 years ago.
One further advantage of this approach is, the prosound midbass driver can have enough power handling (both thermal and mechanical) that you don't have to protect it with a high-pass filter, so you won't need that source of possible coloration in the signal chain.
Best of luck with your quest.
Duke
dealer/manufacturer
