Life After Your Magnepan’s

One of the reasons Maggies sound so good is that they generate a lot of spectrally-correct backwave energy. When placed well out into the room, that backwave energy arrives after a relatively long time delay, which is desirable. This mimics, on a smaller scale, what we find in a good seat in a good concert hall: A time-gap in between the direct sound and the strong onset of reflections. According to researcher David Griesinger, the ear being able to separate out the direct sound from the reflections is highly beneficial, and is largely what differentiates a good seat from a bad one in a concert hall.

In a home audio setting, there is a competition between two sets of venue cues: The venue cues on the recording (whether real or engineered); and the acoustic signature of the listening room. In order for the venue cues on the recording to dominate our perception and enable that elusive "you are there" illusion with a good recording, they must be presented effectively, while the listening room’s inherent "small room signature" is minimized. The backwave of the Maggies can present the recording venue cues effectively, and the long time delay from proper placement tends to minimize "small room signature", so Maggies set up properly can be very enjoyable.

One of the things an acoustician does in a home audio setting is minimize the early reflections while preserving that energy so it can come back as later reflections. This is conceptually similar to what a good dipole does when set up properly.

Because it is spectrally correct the backwave also enhances timbre, which again is something reflections do in a good concert or recital hall.

I realize none of this speaks directly to the question of "what to get after Maggies", but perhaps awareness of what the backwave can contribute is helpful.

Duke

@audiokinesis   Thank you for your very helpful post. 

Try the largest Spatial Audio model you can afford.

If bass is too light, they can be augmented with open-baffle subs like those designed by GR Research. 

You certainly have a large room for any Maggie if you like going louder than 90 dB cleanly and forget about bass below 40 Hz with any degree of dignity.
I owned Tympani IIIs back in the mid 80's. I drifted back to Acoustat 2+2's with subwoofers because the detail was better in the midrange and with the subwoofers was a significantly more powerful set up. 
If you wanted the ultimate in a room your size I would do Sound Labs 845's with 6 subwoofers placed equidistant across the front wall. That would give you the ultimate sound stage and cruise effortlessly at 110 db if you were so inclined to destroy your ears. You can add subwoofers to Maggies but the effect is not as dramatic as adding subs to a full range ESL. With Maggies you are only improving the efficiency of the woofer panel. With a full range ESL you are improving the efficiency of the whole thing. 
I love Maggies. In their price range they are hard to beat if you like the presentation of a tall dipole but if you can afford an 8 foot tall ESL and can put up with the size there is no more accurate or detailed loudspeaker. If you match them up correctly with the right subwoofer array yo are in another league altogether. I have listened to Wilson's, Magico's and YG's and they are all great loudspeakers if you forget about the price. But, they can not hold a candle to full range, line source ESLs with subwoofers and considering Sound Labs 9 or 845's are a fraction of the cost it boggles the mind why anyone would by them. 

The one speaker that will truly amaze you is Sanders Sound.
Roger Sanders makes one product in his Colorado shop and
it is shockingly superior to everything else. $17k.
Buyers get a lifetime warranty and a 500 watt stereo Amp.
Read up and watch his videos. He know of what he speaks.
My dogs about freaked out when I demoed them. Oh yes
he uses transmission line bass so you wont feel shorted.