So I got the FD5. It's only been a couple of days so my opinion will most likely change.
The soundstage is as impressive as reviewed, very holographic. It's a very natural, organic sounding earphone tho, clearly aimed at being musical in nature.
Bass is big and voluminous, good quality tho, but occasionally a little loose. A lot of the detail is in the sub/mid bass, lower mids and it is impressive. So drums, bass/cello, electric guitars, etc. all have extra weight but still sound very detailed.
Mids do sit back. It does veil the upper mids slightly and certain instruments or vocals I'm used to hearing are hidden ever so slightly or a bit lightweight in body... like a feather. Instruments/sounds that sit central/upper mids and lower treble regions mainly can be a little restrained.
It's V shaped but i wouldn't say it's overly extended in the treble, in fact it's pretty smooth. Lower treble is a little veiled as discussed.
The treble filter size is a little slim which doesn't give you much in terms of tip rolling with tips you have.
With the main filter:
Wide bore far too much bass emphasis
Balanced tips are a little too laid back adn veiled.
Vocal tips a bit better and take a little thickness out and adds air.
Final E tips a bit more balanced, but for me don't get the best out of them.
SpinFits do the most to mellow the big bass out and take some of the thickness out, but at the expense of some sibilance and warmth and a little sharpness in the upper treble. It does add some greater space throughout and can help mids shine thru a bit better It's probably the most detail focused.
It might sound like I've ben a bit overly negative, but it's a sound most people will enjoy as do I. I'm aware detail and microdetail can be different, but apart from the very detailed low end, i was hoping for a bit more in the mids and treble. There's definitely a veil there IMO and i find some parts of music i know to be held back. It's FAR from lacking tho as it does bring out parts in the low end I haven't heard, and is a step up from the FH3 as it sounds way more natural. The FH3 is brighter in comparison so does have bit more bite up top and more detail in this region is a little more immediate. Bass on the FD5 is far bigger as is soundstage. They share a similar signature until mids and upwards.
It excels with electronic music, keyboards sound amazing at times. EDM. Modern pop. Bass driven music. Jazz is pretty big and bold.
Classical music some sections and instruments get more focus, strings, percussion sound meaty and extremely natural. More delicate sections like woodwind and brass can be a bit too light for me. Separation does struggle a little bit with the sub region being more focused.
Funnily enough, I looked at the size of the filters and realized i had a budget earphone Monoprice MP80 that had filters and they actually fit perfectly. One of the filters actually takes some of the lushness out and tames the bass a bit, the only difference it takes a bit of the musicality out at the same time.
. Tried the xelastecs on FD7 but sadly they weren't a good match. 
