I have an M5 up for sale actually. Funny enough to your guys comments, I went from a custom to a universal. Their universal just fits so well one of the best fitting IEMs to me.
My problems with custom -
Shell, I broke the shell once with just clacking them together. I do not like feeling like I need to baby my IEMs and can't just use them whenever I want wherever I am. I don't throw them around but sometimes I take them off and hang them on my neck or set them on a counter for a minute or just normal life things.. I can't always be fearful of breaking them and thus never use them.
Second, sound. The bass was way too overpowering in the custom. And I didn't get the adjustable module custom so I was stuck with the module I had. I know this varies based on ear size but I guess my ears are rather large because my shells were huge. And I always had a very overpowering bass in my custom that took much from the spacious presentation.
Universal fixed this. You are correct, FiR using tubeless is a great design for low end frequencies. Low end waveforms are very long waveforms and take a lot of space in a room to fully complete their wave cycle, this is why often 2 channel speakers will not produce bass accurately. If the room isn't big enough the waveform hits a wall and will bounce back against itself before completing it's wave cycle, thus creating Phase filtering and cutting out even more of the sound. And if the room is too large, the listener will not experience so much the impact and power of low end though they'll hear it's complete sound just without the density.
In IEMs it's very very difficult to get true low end and bass. To me, the M5 is the best low end I have ever heard. Full stop. To as close to proper reproduction of low end and thuroughly enjoyable. However, at times it isn't as fast as needed if you're listening to complex metal or high speed rock etc with lots of kicks, it seems to not keep fully up and misses punchiness of many of the hits. The Nio is more responsive in this area.
The second thing about the M5 to me, the size of the soundstage. Width and depth. When I first got the M5 I demo's nearly every single high end IEM in Asia at the end of 2019 and settled on the M5 because it was at the time nearly the best for my tastes. But when I heard the Nio, I though most of the M5 I prefer over it, one thing stood out to me. The size of the soundstage and how it helped give everything amazing space that just added to the music. Lacking Estats was important to me, I became in love with the sound done properly, but the M5 didn't have the same large soundstage and I just kept realizing how everything felt cut closer and thus sometimes could feel a bit congested. Not by technicality was it congested, just by the fact that it could have used more space. Thus my hunt resumed this year with the M5 going up for sale. Though I love the durability and the customer service of FiR, (I think FiR is representing what should be industry standards, longest warranty of 3 years, high insertion ration of over 5k on their RCX connectors, best stock cable to come with IEM, and amazing service team, they set the standard to me.) I just wanted more space and the Sultan definitely has it in spades.
The Sultan's low end doesn't best the M5 but it does good enough withing it's whole sonic landscape that I've been quite happy with it. I still am addicted to slightly more honey mid range vocals and such like with the Elysium, but as a whole package the Sultan has been the best I've had hands in yet to my tastes.
My perfect IEM is basically a Elysium with DD low end.
Estat highs (Done right, BA just doesn't sound as good anymore), DD low (As an engineer I am too aware of good low end, BA does not trick me no matter how good I am used to real air and space)
And honey silky mids - DD here is an amazing choice but you have to blend it with a DD low for me, or something like open cap BA I have been thinking might do it close enough.
And finally, very large and spacious soundstage that will accurately represent the room of the recording. Not artificially exaggerated where you get singers pulled way back in the mix when they're not meant to, but also not limited where everything sits withing a certain width infront of you - I desire truly all around you and extending well past your eyes periferals.
As close to that as possible has been my goal and then I stick with and am a happy bear
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@Wyville if you want to demo an M5 we could maybe set something up before I've got it sold, not sure how well itd go though because I'm currently in US, idk if that's an issue
we're so overlooked here in the EU
