Got spoiled too. Been loving my hd800. Wanted to try my k701 and hd700 again just to mix things up. Man it is hard to go back. Upgrades seem subtle but downgrades are way more noticeable it seems. Still waiting on the d70 dac. Been using the arc with thx 789 for a few days and to me it feels smoother and more subtle as compared to the arc alone. Will try to do some comparisons later on. Love this new hobby, thanks again Alan
Awesome!

Pretty darn nice audio equipment you got

Yep THX-789 + Arc's DAC sounds faster, you can notice how the dynamic range (how goes from loud to low noises) is increased. Pretty awesome, the true power of the THX is unleashed when you pair it with a balanced DAC, but this is audiophile territory, you won't find any gaming edge, however is an outstanding experience for Hi-Res Music and movies.
About the MixAmp Mic, the Streamer profile on the latest MixAmp has kind of aggressive noise gate (kills background noise but also the voice) Night mode is a good alternative on a less agressive noise gate. Just remember to
sync your device to apply the changes.
DanielClem well you have on your hands a very solid legendary MixAmp, no wonder why you haven't changed. After that MixAmp has improve only on decoding 5.1 effects and the mic quality has gotten worse and bit better on the latest releases.
Well, the small and safest step on which you find a huge difference is to switch your headset, for a headphone, the SHP9500 is the go-to recommendation, adding a v-moda boom mic will turn it on a headset with one cable plug, just like your current A40 but with a BIG sound quality difference.
Other recommended headphones are: HD599 (Black/Silver amazon exclusive) has more bass and will be more fun to play with it, and Philips Fidelio X2HR are a bit more expensive yet worth it.
As you may read it before, bright headphones meaning high treble are more useful for footsteps (sound-whoring) but tiresome for gaming, warm or bass heavy headphones are better to enjoy explosions, reverb on caves and music soundtrack from solo campaign experiences.
The next step will be to improve your DAC the device that makes the sound. This is where you have to take into account your console or platform, specially for the next gen consoles. I find it very weird and shady that there is no SPDIF option, I hope they change their mind on it, is not fair to keep limiting the costumers or force them to upgrade to other inputs.
Regardless, independent no-platform or driverless audio devices always will have an option to hook up with our consoles, sound has to be turned to analog in some point and all the better affordable up to the high end sound devices has an analog input.
About immersive sounding experience.
You can take two routes, go with a high res stereo signal or
fake reverb 7.1 surround.
As has been stated before, you don't need a saturated alter audio signal with reverb to feel a 3D stereo experience. In life we have two microphones (our ears) and the best engine or sound encoder: our brain. Here an example of it, get your earpods or any straight stereo headphones and hear this video:
Virtual Barber Shop, that's called
binaural recording, uses two microphones even with fake ears

to recreate how sound is perceive for our head, cranium and ear lobs. Best Triple AAA games has Binaural Mix recordings, some called 3D Stereo, Enhanced Stereo, Binaural Stereo all the 3D surrounding magic has been made on the mix, you only need a stereo headphones.
Contrary to a 7.1 surround device, that has to take a stereo signal, made a makeover, just like when you take a picture and use filters to make it look vintage or old, etc... you alter the quality of the source to give it an effect, and that's whats happen with MixAmp Surround, SoundBlaster X3, X7, Steelseries 7.1 headphones, and all that crap.
Now, the best bet for sure is to get your a great set of Stereo Headphones good quality and a DAC that interprets sounds clearly with a well recorded and tuned source coming from the game.
I'm not a stereo purist, I do think surround sound has its place, like season, spice however very few devices does it right. like the Senheiser GX1000 -which is not compatible with consoles- and the Dolby Atmos filter on Windows. I hope next gen consoles allows us to add this filters on games.