[TheOneInYellow]

1. REFERENCE filter is a lie
2. MID-HIGH BOOST filter is everything !

Took ages to get to grips with my N5005 via both FiiO M17 and included AKG Bluetooth neck cable, but seriously, reference filter (lightly) sucks out the upper-mids and lower treble, especially on female vocals.
For further context, I listened to my AKG N5005 IEM's using included balanced cable, Eletech Baroque eartips, FiiO M17 with external battery power bank at High Gain, and native resolution.
When comparing to my T+A Solitaire T headphones, they were run with the same setup as above, except using Solitaire T's included passive balanced cable, and M17 set to Enhanced Over-Ear Mode (highest gain).

Tested the AKG N5005 with reference filters on many female vocalists, including but not limited to: from Adele, Beyoncé, Ilaria Graziano (a friend of famous Japanese composer Yoko Kanno, and Graziano sung on quiet a few tracks from Ghost in the Shell: Stand Alone Complex soundtracks), Beth Gibbons, Billie Eilish, Miley Cyrus, Solange, Kelli Daytona (lead singer of Sneaker Pimps 1994 - 1998), Becky Hill (collab with Chase & Status on the record Disconnect), and some other singers.
However, listening to Hannah Reid from London Grammar on the album Truth is a Beautiful Thing @ 24 bit /44.1 kHz (2017, Metal & Dust~Ministry of Sound) (stream link) broke me this evening on my listening session after failing to tolerate the reference filter any further.
To explain further, the first song where I simply stopped listening mid-song and went "...no" was Wild Eyes. After a short recess and getting some water, tried to continue the album. When I got to Hell to the Liars track, I was infuriated, and decided to do tests with my T+A Solitaire T to confirm how her voice should sound. For context, my Solitaire T are my only other reference headphones, and fairly neutral, natural, buy have some warmth to the bass region, and amazing treble response.
Not only was the AKG N5005 reference filter a huge affront to Reid's vocals, it also made her sound wrong, and I hated hearing London Grammar on the N5005 with reference filter.
I tested my T+A Solitaire T in balanced mode with my FiiO M17 for comparison, and though with this setup I lost soundstage in almost every direction, at least Reid sounded far superior.
Sure, the truth is it may not be such a big change of frequency response, but sometimes that can be enough. I got used to the reference filters on my EDM, rap, pop, industrial metal, and trip-hop albums, but I during that time, I became increasingly aware of my dislike of female vocals or high-pitched male singers using the reference filter, and this was colouring my opinion of the N5005.

Thankfully, and as you all very well know, the N5005 has a party trick; multiple filters!
Looking at this thread and noting that, for these IEM's, the mid-high boost filter is the one that follows the Harmon Kardon iem curve, I decided to give them a try.
WHAT a difference, immediate and effective. Though the treble section does not match my T+A Solitaire T (nor does the bass texture, or midrange detail...ish), at least Reid now sounds more correct and her voice beautiful again.
Such a small change in frequency response can have such wild changes of aural perception and physical frequency change, and here is a mighty example!

I can really relax to London Grammar and Sneaker Pimps with the AKG N5005 + mid-high boost filter, and enjoy the expanded soundstage (one of the biggest negatives of my T+A Solitaire T) comfortably.

Anyway, going to continue to listen, but thought to post my observations here