Well, I'm quite familiar with the Axiom M80 and the Emotiva speakers - I haven't heard the Swans for myself, so I can't comment on those.
First up: what are your room dimensions and how far away are you sitting from your speakers?
You have to allow adequate distance for all of the drivers in a tower speaker to "sum" together into a single, coherent sound source. Sit too close and you can wind up with audible separation between the drivers.
Now, the recent backlash towards Axiom aside, their top level speakers are still very good performers. After listening to the entire Axiom lineup for several years, however, I have to say that I really only think their top models should be considered. That new VP180 is stellar and matches seemlessly with the M80 towers. The other two center speaker options have always sounded a bit "off" IMO. I've never been able to whole-heartedly recommend Axiom's center speakers. But the VP180 changes that! The thing is, you really need to build a matching system around the VP180 and that means M80 towers and QS8 surrounds - so the most expensive package that Axiom offers.
With that top-of-the-lineup package, you get a very seemless and highly accurate speaker package. Despite their unwillingness to participate in the subwoofer shootout (not that I would recommend any of the Axiom subwoofers anyway), their anechoic testing of their speakers basically boils down to one, nice thing - whatever the final outcome in your room, Axiom's top model speakers won't be "to blame" for any anomalies. The M80 towers and VP180 center act as very neutral and transparent pieces of equipment. You can thus, tune their response to your room's particular acoustic characteristics and be quite certain that they will respond in a very predictable way. The M80 and VP180 will not be ruler flat in your room on their own. But they are ruler flat in an anechoic chamber. That means that what the speakers themselves are producing in terms of output is accurate and reliable. So from that baseline, you can adjust the rest of your equipment and the room's acoustics in order to achieve your desired results. You are not having to work around the speakers having some sort of "character" or their own.
When you step down from the top line models though, while Axiom still aims for neutral and transparent performance, they aren't able to achieve it to the same high standard. Those VP100 and VP150 center speakers are just not right and the other tower and bookshelf speakers have little quirks to them as well. So... if you go Axiom, go all the way and get their highest end models.
The Emotiva speakers are very, very close to being professional studio monitors. They have the same sort of adjustability as pro monitors, which means that you can somewhat tailor the speakers to your room, as opposed to the other way around.
Unless you are planning to run your system without a subwoofer though, the 8.3 towers are not really necessary. The 8.3 towers act essentially exactly the way you would expect them to based on their looks - they are a large bookshelf monitor perched atop a couple of bass drivers! If you have a subwoofer (or two or four) in your system, then you will literally not be using those bass drivers in the 8.3 towers! Instead, you could keep the cost lower by using the 6.2 large bookshelf speakers for your front L/R or the even more powerful 6.3 speakers with three of them across the front.
The only issue I have with the Emotiva speakers (aside from their VERY plain looks and larger-than-you-might-think size) is the tweeter. Don't get me wrong - it's not bad. But it just isn't that great a tweeter. It hits its output limits fairly easily (again, really reminds me of a nearfield pro monitor). And its extension before hitting break up or becoming sibiliant isn't anything to write home about.
So, despite their size and ample ability to devour amplifier power, I actually think the Emotiva speakers are best suited to moderately sized rooms - akin to a professional mixing room. They are very neutral - they will tell it like it is. And you can adjust their output to compensate for room placement and distance - which is always handy.
The ERD-1 surrounds are a treat though - they nail the dipole design and effect. What I like best is that they adhere to the 2nd order 80Hz design (other than the 8.3 towers). They are one of the very few speaker options out there that adheres to this design. As a result, they work PERFECTLY within a THX setup where the receiver/pre-amp uses a 2nd order high-pass on the speakers and a 4th order low pass on the subwoofer. With the natural 2nd order roll-off of the speakers themselves, you get the intended 4th order slope on the bottom end of the speakers at 80Hz. This is how THX was MEANT to be implemented, so that is a strong plus for the Emotiva speakers IMO. If they had a better tweeter, I'd praise them to no end!
