Crinacle recently (this just passed its 1 year anniversary, lol) did an interview about how his collaborations (KZ CRN/ZEX Pro, Moondrop Blessing 2: Dusk, etc.) kinda came to be: https://www.youtube.com/watch?v=-2PrHgoU0Q0&t=249s

Search up Delta Fyre, Hi-Fri Audio, etc. Those people on Facebook that do teardowns/dissections/etc. of IEMs. They'll show you the drivers being used, the dampening measures, the crossovers, etc.

Right now the Simgot EA500 is receiving a lot of hype and due to the removable nozzle, some people are doing tuning foam mods and so on. Some people are also using the removable nozzle of the Moondrop Kato and so on with the EA500.

To replace the filter/mesh/et cetera, usually those are like $2-5+ from AliExpress. So just need to wait a few weeks. Maybe they're on Amazon too, check around there sometimes, you might need to use specific keywords for them to show up.

Usually people use say 400-500 for the size/etc. of the meshes/etc.

See here for a bit more info about tuning foams/meshes/et cetera: https://www.reddit.com/r/headphones/comments/vpljd3/dioko_update_good_to_see_crinacle_taking_a_more/iekb7li/ and https://www.reddit.com/r/HeadphoneAdvice/comments/11wu2qo/losing_volume_in_left_earbud_after_only_2_months/jd3q92t/. Check RikudouGoku's posts/threads on Head-Fi and HiFiGuides.

Some companies are also producing DSP versions of their IEMs, but people say there's inherent delays/interferences/etc. with playback and like buzzing/static/etc. with them. See here for some threads about those DSP IEMs: https://www.reddit.com/r/headphones/comments/11xvoqu/moondrops_dsps_defective_quarks_dsp/ and https://www.reddit.com/r/headphones/comments/1164nep/moondrop_quarks_dsp_not_quite_as_good_as_we/

Here's Timmy from Gizaudio talking about the DSP IEMs issues: https://www.youtube.com/watch?v=wKs_-d26WXA

Don't forget ear tips. They can make or break the sound quality due to the treble resonances from the insertion depth, et cetera.

These days a lot of ear tips are medical grade silicone and they are often so thin/etc. that the bass is noticeably altered or reduced.

Info about the Moondrop Spring, TRN T, ear tips that can warp easily to break the seal/fit, et cetera: https://www.reddit.com/r/HeadphoneAdvice/comments/11spulp/believe_in_audio_improvement_claims_of_eartips_or/jcfo5z1/

Click this sentence for more info on the importance of ear tips sizing, dimensions, et cetera.

Click this sentence for more info on foam ear tips durability and sound changes.

Click this sentence for comfort and everything with ear tips.

Click this sentence for how to put ear tips on wide nozzles (basically aim it at different angles and force it, be careful not to overdo it as it can damage the core/stem/stalk/etc. of the ear tips).

This is how you should use Etymotics or really any IEM or TWS earbud to make sure you have that good/perfect fit for that vacuum seal (necessary for the bass to be properly produced): https://www.youtube.com/watch?v=8KwXEqe6Gq4