I do not think it is correct to state your modded pair is the original ie800 or ie800s and make comparisons called ie800SvsFiio...etc
Acoustic chambers - (front and back) make 50% of IE800(S) sound signature, it is very sophisticated and unique system (senn engineers knew their perversions, that's for sure))
The front chamber in your mod has nothing in common with the original, and back chamber is at least beccme much bigger.
I even suppose that there are no genuine drivers inside. I've seen the modded ie800 supposingly from the same shop some time ago and it contained no genuine ie800 drivers. I liked the sound, it was pretty descent, not at the same level as some cheap fakes out there, but at the same time not close to originals. Just another iems in the same enclosure.
Fair comments. The modded IE800s has a different/larger front chamber, and the back volume may be larger, or similar, depending on how the driver is placed. The helmhotz resonators in the rear may, or may not be tuned same as original. I believe it is expected that the end result is no longer original factory, due to the physical changes, and thus the SQ will be different, and the user will have to be aware and and take this into account. It is prudent to mention this, though, so there are no surprises. So yes, be aware of all the above. My comparison with the FDX is against a modded IEM that looks like the IE800s, and is not a valid comparison with an original IE800s. However, I do have/had an original IE800, so have an idea of the horrible ergonomics, and the excellent sound of the original.
Original drivers or not, as I mentioned, I of course had the same worry, and I took a chance with the purchase. I have no way to verify what is in mine. I can only decide based on whether the sound is worth the effort, for what I wound up owning.
(The shop will have a real IE800 for sure, though. The one I traded in.)
In spite of all the above caveats and concerns/worries, I am happy with my purchase. I paid a reasonable price, along with a trade of the IE800 which I was not getting any use out of.
Whatever these are, real drivers or not, I am enjoying them tremendously. If I could be sure that the driver is original, it would satisfy my OCD, but I am not going to let that affect what I am hearing, and will judge these based on the sound/enjoyment I am getting out of them.
I agree that my posting was questionably relevant to this thread, and had not much to add regarding the FDX topic, so I apologize for creating "noise", which I would also think was irrelevant and confusing, when I observe similar postings in other threads. So no more postings about this from me. Anybody with questions can PM me.