Anthem ARC - Well, it's not that great.

What firmware are you using?

Maybe not super, but better than the Audyssey competition. I have been running an MXR310 with updated software quite happily as HT in two houses now in 5.1   Could also be that Anthem amplifier sections are better than most in the price range.  I have no interest in Atmos and really would be happy with 3.1 as I just don't care much for special effects.  Yes, I have heard a super high end 9. something with 3D and I would not pay 1/10 the price for it. It is not my music system. 

One problem is many rely on the DSP to fix speaker problems where it really is better just on lower frequency room issues. EQ alone won't fix room imaging or crappy speakers. The better you start, the better the result. 

Another problem is when many people first experience getting the humps beat down, it seems a bit flat.  No more 4K boost  and no more bass boost. Those issues may be easier to see the difference playing music, not movies. 

Perfect? No but I am not ware of anything better I could afford. Mini-DSP is the only alternative I would pursue if my Anthem died.  It may also be difficult to separate  what is DSP and what is the DAC and amp. Well, might go to 3.1 and the Schiit SYN. 

The mic was designed when ARC only handled low frequencies. As the software improved, the mic did not change.  Without decrypting the calibration file, we'll never know. I imagine it is the same Panasonic capsule ( or clone) as in most cheap condenser mics

Yeah, I used the Anthem ARC in the form of the Martin Logan Perfect Bass Kit, just for subwoofers, and the results were that I much preferred subwoofers without any room EQ.  
If you’re curious, you can read about my write up in the speaker section here:

https://forum.audiogon.com/discussions/subwoofers-and-electrostatic-speakers

To be clear, I would sum up my complaints in two issues:

• Immersiveness
• Bass response

Listening to well mixed DVDs I don’t feel surrounded by the environment. I feel subjected to it. The bass also doesn’t feel well integrated with the rest of the system. I can hear all 5 main speakers, but I don’t feel surrounded. The front channels never fully merge into 1 audio presentation, and the rear speakers also feel separated from the fronts.

In my experience, this is something you can do with 5 speakers alone, you don’t need Atmos to get to this level of performance. Just good speakers, a good room and careful EQ.  An approach at least a little validated by Floyd Toole's writing on "room correction." 

My personal approach to EQ is very different from Anthem. Anthem picks an ideal curve and tries to get all speakers to match it. I used my mains as the reference and made the 3 remaining speakers match them. I also set the bass to go down to 16 Hz and descend about 1.25 dB/octave.

Another way in which my approach differs from Anthem is that I only use 1 measurement point. Trying to set all 5 speakers to an ideal curve, across multiple measurement points may be correct on average and exactly wrong where I listen.

Lastly, when I do EQ I do so sparingly, attempting to use the least amount of filters and least amount of correction as possible, giving myself more freedom in the bass to fix room modes than in the mid to treble.

For all these reasons I want to try a Marantz HD processor next. The advanced Audyssey levels let you craft your DSP curves completely by hand.

An interesting topic is brought up above, which is what all the extra speakers are for. Are they for effects or immersion?  This argument was compeltely dominated by Dolby in the days of Dolby Surround (i.e. ProLogic for the home buyers).

Dolby Surround was 100% aimed at effects. Wow factor. The internal steering mechanism prevented mixing engineers from even attempting subtle immersive audio environments. They encouraged fly over type of effects, oddly sometimes always going in one direction. Alternative decoders IMHO may do a better job for that 2-channel multiplexed era of movie experience.

Today in the era of discrete channels and now even object based audio encoding this capability has finally been wrested from the electrical engineers and put back into the hands of the mixing engineers where it belongs.

That is not to say movies are better mixed, they are not always, but I think the chance of having spectacular audio environments has certainly come a long way.