ML's are relatively bad as has been noted. Newer Quads aren't as good as the 57's or 63's. Listen to a pair if you're curious why. Quad 57's are really outstanding but not for everyone (meatheads may not approve). 63's are good and some prefer them though they lack a bit of the dimensionality and richness of the 57's. They play louder and are more extended. They also implement the most advanced/coolest crossover ever devised. Not as listenable in my opinion. There are potentially better/different electrostatics besides the Quads (Apogees [less detailed, more extended], Staxs [more detailed, zero bass, perhaps the hardest speaker to drive ever], Soundlabs [great but maybe a little incoherent, out does the quad in certain aspects], a few other notable ones I'm forgetting, and then there's the KLH 9's, the Sony SS-R10 and the Beveridge Model 1 and 2). I too scoff at hybrid designs like Acoustats (and ML's) for reasons noted above. If wanting to go that route, a transmission line sub would be the best bet (or massive woofers eg. HQD).
The only (somewhat attainable) speakers I'm really into are Quads, Staxs and ERAudio/diy electrostats. Some don't like the sound of electrostats as they don't play loud. The next closest thing in the detail dept are horn speakers (coaxials being the best though expensive to produce) which achieve some of the detail of electrostats and can play louder (the loudest of any variety of speaker). They also throw a better more coherent soundstage and have a larger sweet spot. The only ones that are remotely comparable to electostats however are either massive to achieve high sensitivity (custom made/old western electric horns for instance) or very expensive due to difficult, toxic, scarcity of resources costs needed to produce beryllium diaphragms. They're not as refined as great ES speakers though. Unity horns, Gedlee designs, and other diyish innovations are of interest though at the end of the day the drivers used simply aren't physically capable of the level of detail that an electrostatic driver is capable of reproducing.
Regarding the bass issue with electrostats, the distance of the stator gap (as well as the diaphragm thickness and the conductivity of the coating material and quality of crossover if present and so on), determines how detailed/how loud (without noticeable distortion) the diaphragm can operate. Martin Logan designs for instance, tend to implement a larger stator gap to achieve greater dynamic performance (thus in theory appealing to a larger consumer body) yet this comes at the cost of detail. A couple new designs use a staggered system where the bass transducers feature a larger gap and the mid/treble transducer feature smaller gaps. This enables more dynamic and extended bass performance (and better than that achieved by any traditional driver).
Ditto on the new Quad stats:junk. The' 63s are often bargains vs. the '57s and can be modified to sound even better, if they aren't already (most are, also the '57s). The only thing I have to say, about the older Quads is that they won't get the job done for bass lovers, nor will electrostats with active subwoofers. The latter sound worse with the subwoofers than smaller models without! You really have to be a mid-range purist to love the older Quads. The newer Quads are cheap junk, made in China. Read the recent post by Charles Hansen (Ayre) on AA: http://www.audioasylum.com/audio/speakers/messages/31/319722.html .