A flat speaker response IMO is ideal for longer use, which is why studio professionals can and do use speakers all day long which have as flat a response as possible. In my own experience, having a flat frequency response means fewer random frequency spikes, which people are can be very sensitive to even without realizing it. That means the benefits of a flat response are two-fold: you can listen at higher overall SPL and hear more detail in the music, and also feel less fatigued because there are fewer sounds and resonances that are (even subtly) out of place.
Some find speakers with a perfectly flat response too bright, but this speaker also has built-in DSP, which means you can dial in a warmer “tilt” to the sound (of just a few dB from the lowest to highest frequencies, in a consistent downward slope), which may take some of the edge off. You need an iPad to use the Neumann app, though, as far as I’m aware.
I think your main challenge with that will be that the integrated DSP in these speakers can only control the frequency range above the crossover with the subwoofer. So you can get a rough balance between the sub and KH80s using an SPL monitor (which is what I’ve done), and/or use software EQ for the bass, but getting the right balance with the latter may be somewhat tricky. Also, if you use both software EQ and internal DSP, you will lose some headroom for max SPL. Maybe not enough to matter for desktop use, though.
On the other hand, if you’re not planning to use the DSP (which, if it matters to you, may also undo the benefits or purported benefits of filters, DSD & high sample rates at the playback & DAC stage, as the KH80 is 48KhZ internally), you might be better off with a pair of KH120s instead of the KH80s-plus-sub. They’re analog, and you can just use software EQ as needed to control the whole frequency range. You won’t have quite as deep bass extension or impact as with a sub, but it will probably be cleaner and tighter, and still sound excellent for all genres.
If you do go with the sub-plus-KH80s, the most important issue in an untreated room will likely be the placement of the subwoofer, which you can model with REW to minimize room modes.
I should add a disclaimer that I’m far from an expert on any of this, and still have a huge amount to learn, but I do have both the KH80 and a pair of KH120s as part of a 5.1 setup in a small untreated room, and also use the 120s in my untreated office as desktop speakers for video work and electric piano. I notice a difference with the sub for some music, but most of its impact comes from the LFE when I’m watching TV & movies.