I'll split the audio performance analysis into two parts - gaming and music. Even though the headset produces the same sound regardless of what it's being used for, you won't necessarily look for the same things while annihilating your virtual opponents as you will when listening to your favorite tunes.
Gaming
The Asus Cerberus V2 sounds exactly like you would expect a gaming headset to sound. Meaning, the emphasis is completely placed on the bass. The bass is massive, loud, and explosive. During one of my Battlefield 1 multiplayer sessions, a friendly heavy tank came up behind me and fired its front cannon. The Cerberus V2 slammed my ears with the bass so hard I instinctively went prone, which is something I normally only do when I see no other way to get out of a situation alive.
Unfortunately, as massive as it is, the bass isn't very quick or accurate, especially in the lowest sub-bass range (anything below 60 Hz). It also keeps spilling into the midrange, preventing you from picking up and making sense of finer details, such as footsteps. Combine that with a soundstage that isn't particularly wide and you get a strange experience with spatial positioning. I was usually aware of the close proximity of my in-game targets, but most of the time, I wasn't sure from which direction they were trying to get a jump on me. That left me with a slight feeling of paranoia - I knew someone was there, but didn't know exactly where, so I kept trying to look in all directions at once. When your in-game surroundings are quieter, the spatial positioning becomes much easier.
As for speech, I had no trouble understanding what my teammates were telling me, even while under heavy fire. The upper midrange seems to be properly taken care of.
With all that being said, if subtlety is what you're after when choosing your gaming headset, you'll be better off looking elsewhere.
The passive noise isolation isn't perfect - the seal isn't tight enough for no sound to leak out or come in at all - but I don't see it as potentially problematic unless you plan to use your headset in a room with people who can't stand a single peep coming from your direction.
Music
The overall acoustic presentation of the Asus Cerberus V2 isn't at all natural. I would describe it as dark-sounding and veiled. Have you ever put your headphones on while wearing a hat that covered your ears? That's the kind of sound the Cerberus V2 produces.
Quieter music, especially that with lots of piano or strings, doesn't sound pleasant. I didn't find much joy listening to guitar-heavy genres either, due to the lack of clarity and sparkle in the highs. Only after queuing up artists like Sage Francis, MC Dälek, Run the Jewels, and El-P did it dawn on me what the Cerberus V2 is supposed to be used for as far as listening to music goes. Utilize that fat, wall-shattering bass to enjoy your favorite rap, trap, and dubstep tunes. You'll forget about the existing technical drawbacks of the Cerberus V2's sound presentation in no time.
Interestingly enough, the Cerberus V2 does benefit from a couple hours of burn-in, so don't judge the sound quality until you've used the headset for a couple days, as it does improve to some extent. The impressions I've outlined here were all written after over thirty hours of testing, of course.
During testing, I tried connecting the Cerberus V2 to a couple external DACs with integrated headphone amps - namely, the FiiO E10K and X5 (in DAC mode) and Cambridge Audio's DacMagic XS. Can it benefit from such devices as compared to simply being plugged into the motherboard? Sure. The bass gains a bit of much-needed tightness and a bit of warmth is added to the overall sound. Would I recommend getting a dedicated DAC/headphone amp only to pair it with the Cerberus V2? Nah, not worth it.