INITIAL IMPRESSIONS!
Okay, I've spent a few days listening to these (and some burn-in time on a playlist set to very loud) and going to my old set of Atrios to compare.
The FS Spectrum Series G10 has the Future Sonics DNA for sure. The basic tuning is like the Atrio, they are clearly and immediately related to one another. That means real sub-bass really filling in the bottom end of the sound and a monitor realism in the midrange and treble, with no artificial spikes in the treble.
However, the SS G10 is better in just about every way both sonically and otherwise than the Atrio. Head to head with the Atrio, the G10 is more detailed, with a crisper, tighter sound from end to end. The treble is more prominent and the midrange cuts cleanly and easily to sing through the powerful bass, which somehow doesn't encroach on the mids.
Isolation is better, too. The soundstage, for me and my experience, was good for an iem and had good depth, but let me say this: Some people complained about the soundstage for the Atrio (which people who had Future Sonics' own custom silicone sleeves discounted as being a fit issue). The universal tips are exactly the same ones here and the excellent full-custom silicone are too. So, I'd say soundstage here will probably be intimate on the G10 for those for whom the Atrio was intimate. I would highly recommend the custom silicone sleeves.
On the outside, the housing is more sturdy, being coated metal, the cable is beefed up and the strain relief has been redesigned for added strength. It's very wearable and designed to be over-ear.
All in all, it's a different tuning than many iems, particularly armature-based ones, but if you're up for it and willing to take the time to let your ears adjust, it's a sound that really draws you in and reminds me of live music events.