I own Mahlers (and Salons).
Assuming you have a large room (Sumiko, the U.S. distributor, actually recommends Mahlers over Amatis if you have a large room) and are careful about pairing them with the right speaker cables and a fast solid-state amp with a lot of current delivery, they provide a surprising amount of refinement (resolution, coherence, musicality), great soundstaging and enormous slam. They usually will not work in smaller rooms, as they must be placed out from the walls due to the rear ports, and with each speaker having two 10" woofers and two 7" midwoofers (the midwoofers being the same midwoofers used on the Maxx II), they can easily overload a room with bass. The Anthony Cordesman review of the Speaker for Audio and Robert Deutsch review for Stereophile, both of which are available on Sumiko's website (www.sumikoaudio.net), are, in my opinion, pretty much right on the money about their strengths and weaknesses.
I listen to some very challenging orchestral music (30%) and loud blues and blue-based classic rock (20%), some signer/songwriter (10%), as well as smaller jazz ensembles (25%) and chamber music (15%) (and maybe 2%? everything else). I have had my Mahlers since March 2001 and have tried them with three different amps. First, I ran them with my longstanding Bryston 4B-ST, and with Kimber Select 3033 all-copper speaker cables (Sumiko was then demo'ing Mahlers at shows with Kimber Monacle, and Kimber convinced me that the Select would be best -- there is something about the geometry of those cables that brings control to woofers). With the Bryston 4B-ST fed by an Audio Reseach LS-3 linestage and Madrigal 37/360s combo, plus Aries w/JMW 10.5 arm and van den Hul Frog into a Rowland Cadence phono stage, all components hooked up with Kimber Select 1030 all-silver IC's, the Mahlers were VERY good in all ways, demonstrating excellent synergy and an enveloping, musical, potent presentation. The Mahlers are fun!!
I later ran them with VAC Renaissance 140/140 Mk. III triode tube monoblocks and Kimber Select 3038 all-silver speaker cables. Even when run with zero feeedback, this combo was really, really impressive, as it let through the incredible transparency, bloom and timbre that those amps and cables are capable of, while retaining tremendous wallop and reasonable control in the bass. The bass was just a tad looser than I would have preferred with the VAC's (it was about like the speakers with the Bryston), but it was not something I couldn't happily live with (and I did live with it, at zero feedback, for two years).
Finally, I ended up running them with Rowland Model 6 monoblocks with batteries. This was the best combination yet, as the Rowlands are very high current and fast, and are also voiced in many ways like a good tube amp, but with better extension. With the Rowlands, the speakers came very close to emulating, in a largeish room, the scale and dynamic shadings of a full-boar symphonic performance -- very few speakers can do this, regardless of price. If you buy Mahlers, I suggest you get Bryston monoblocks so that you can really enjoy the power portrayal these speakers are capable of delivering. I actually prefer my Mahlers in some ways to the Salons -- for the money, it is truly a lot of speaker.
As for the Audio Physics Avanti III, I heard a pair at a dealer in Chicago about five years ago. They appeared to be set up correctly (you take your chances with too many dealers in this regard) and I really liked the sound: detailed and natural. As compared to the Mahler, the Audio Physic will emphasize bass speed over bass slam. With your solid-state gear, though, I would think that a speaker like the Avant III, with that ring tweeter, could be on the bright, analytical side.
The Amatis are wonderful, but I would never power them with a Bryston. They love really good tubes amps ($10K+). I heard a pair driven extensively by an all-Levinson system at a dealer and they could not have been more disappointing. If you go with Amatis, you may consider moving to something like a CAT tube amp or VAC tube amp (i.e., a tube amp with the power supplies and output transformers to handle a truly tough load -- there ain't many).
The Thiels are often maligned here, and very unfairly, I think. I would happily drive big Thiels with a Classe Omega or other monster amp known for sweetness and midrange warmth. Your very neutral bryston 4B-SST may be too "honest" for this speaker -- it benefits from a big, romantic amp with a substation full of current (think Classe X.5 series or big McIntosh).
Good luck.
