Sorry to hear you have to find an alternative to your Sound Labs! I'm an owner (and dealer), and have searched far and wide for alternatives to the Sound Labs. I have yet to find their sonic equivalent in a conventional package. The problem is, you can hear the box in many otherwise very fine loudspeakers once you've been spoiled by the Sound Labs.
I owned a pair of Crosby-modded Quad 63's for a couple of years, but I must say that in my opinion the Sound Labs are across-the-board better. In particular I have a low tolerance for upper midrange problems, and to my ears there was a slight upper mid/lower treble prominence with the Quads that could put on an edge on close-miked female vocals.
I also spent a day in the home of Siegfried Linkwitz, designer of the Beethovens, listening to his pair. Stunning dynamics and an utter lack of boxy colorations. The voicing and presentation is different from the Sound Labs, though - a bit more forward.
I've chosen to become a dealer for a speaker that's conceptually similar to the Audio Artistry line, but with voicing more reminiscent of the Sound Labs. This is the Gradient Revolution. The Revolution uses dipole loading for the bass and cardioid-pattern pressure-relief loading (via large damped slots) for the mid/tweet module. This gives the Revolutions that elusive freedom from boxiness across the spectrum, and the mid/tweet module is a concentric unit so the sound is exceptionally coherent. The dipole bass loading gives the kind of naturalness and pitch definition in the bottom end that us Sound Lab owners would hate to give up. The combination of dipole and cardiod radiation patterns produce a reverberant field with the same tonal balance as the first-arrival sound, which is another rare quality they share with the Sound Labs. The biggest drawback to the Revolutions may be their price - they only retail for five grand, and so are way below your ballpark. See www.gradient.fi. Don't be put off by the fact that the concentric tweeter is a metal-dome unit; it has none of the hardness we normally associate with metal domes.
Within the next few months the active version of the Revolution (first shown at CES 2001) should be commercially available, and passive versions can be converted to active ones. This would enable owners to add additional bass modules to upgrade bass extension and headroom. The active Revolutions I heard used two additional bass modules per side (retail of around twelve or thirteen grand total), and the presentation was magnificent, especially the rendering of massed large strings (we were listening to Mahler's Third).
Coming from a Sound Lab background myself, the thing that captivated me about the Revolutions is that they don't sound like speakers even in the bass (and in this respect they outperform speakers many, many times their price). Like with the Sound Labs, you can walk all around the room and the tonal balance stays pretty much the same (of course the soundstaging is best down the center-line of the room). Nope they don't have quite the inner detail and nuance of the Sound Labs, but then not much else does. But they do have that relaxing, all-day-listening naturalness.
I'm sure it sounds crazy to you for me to be recommending a five grand speaker (upgradable though it is) as a replacement for the Sound Labs. I sell other speakers that cost more than the Revolution, but as someone coming from a Sound Lab background the Revolution would be my personal choice, preferably in the forthcoming active version with a few extra bass modules.
Let me mention a few other speakers I don't sell that appeal to me as a fellow Sound Lab owner: The Maggie 3.6 and 20 (haven't heard the 20.1 but I presume it's even better); the MBL Radialstrahler; the Rethm; and the Intuitive Design Denali. All of these designs are coherent and natural-sounding, and have very low to non-existent levels of boxiness.
Shoot me an e-mail if you have any questions, and if the Revolutions sound promising enough to you I can arrange an in-home audition.
Best wishes to you in your quest!