The 8331 is a near-field speaker that I use at arm's length. It might lack the lowest bass octave, but otherwise the bass is very precise and punchy (at reasonable volumes). I found the Orbits to be very direct , but they lacked the transparency, the exceptional separation of individual elements in the mix, and the fatigue-free listening experience that the 8331 offers. I really found the orbits too tiring in the long run. Almost annoying.
Precise, punchy, direct, transparency, separation, fatique-free, tiring, annoying. Don't want to argue with that. On the other hand, these subjective impressions are hardly relevant to others, since they don't apply equally to everyone. For example, I can and do listen to the Orbits all day long without any of the issues you decribe. Best thing one can do is translate the subjective impressions to technical parameters as far as possible.
As both speakers will mostly be operating in their comfort zone when placed at arms length, distortion is probably no issue. You are almost exclusively getting direct sound, which means dispersion characteristics are also not a big factor. Probably you get some table bounce and maybe front-wall reflection. If the Orbits are placed right at the wall, the cardioid dispersion will minimize rear-wall reflection. Unless the wall is much further apart than the arms-length, 8331 cannot avoid at least one cancellation notch from the rear-wall reflection. The front-wall will also reflect whatever comes from the bass-reflex port.
This basically leaves on-axis frequency response, boundary gains and the aforementioned reflections as the biggest potential differences. In most situations some EQ will be required to optimize frequency response. "Direct, tranparency, fatique-free, tiring, annoying" can correspond with frequency response. While the Orbit's are basically flat on-axis and offer quite some EQ filters, optimum room EQ can only be achieved with measurements and fully flexible EQ filters. This is not specific to the Orbits. Too much bass can also be tiring. In most situations the bass shelving or near-wall filters of the Orbits are helpfull to counter room gain. I also reduced treble with the Orbits shelving filters.
For "separation of individual elements in the mix" IMD can be a factor. Erin didn't measure it in his 8331 review. Certainly looks good for the Orbits.
With regard to "precise and punchy" bass, I would see the closed-box Orbits with lower group delay in a good position. Orbit's lower distortion in upper bass is also helpfull for precison and punch.
For many people it's hard to impossible to get over the price difference. In hifi shows the price is often the most important spec to convince people of the stellar performance they have to expect from often ridiculously priced gear. It helps to look at the measurements and components comprised in these speakers. Enclosure, electronics, speakers in
Genelec monitors are of similar quality as the corresponding parts in the
Orbits. Yes the Genelec coax speakers are slightly more optimized. But not by a large margin and mostly affecting off-axis dispersion.