As always @Torq is the go to man here. Having only recently bought the 64 Audio U18t’s I can comment a little. Firstly they’ve packed in 18 drivers on each side with 8 Low BA drivers and 8 Mid BA drivers. The other remaining 2 drivers are the much vaunted TIA (Tubless Inear Audio) type. One being for the Mids and the other for the Highs.
As well as this they also employ their APEX (Air Pressure Exchange) technology which is said to help alleviate air pressure build up in the ear canal this minimising listening fatigue. It does this via a plug in modules (apex module) which have vents of varying sizes, depending on which module is chosen. You are supplied with 2 apex modules the m15 and the m20. The m20 offering slightly less isolation -20db hence the m20, with the m15 offering -15db. The differing modules do change sound slightly but not significantly. The m20 offers a little more bass and brings a little more to the lower mids whilst the m15 gives slightly better imaging and highs.
These are just a couple of innovations in the iem arena that have crossed my path. All in all I would say they are very successful ones too.
As for planar iem’s the only ones I have tried are the iSine 20’s. You will of course read much about this polarising iem but it really is a kind of love hate with these. The sound I loved though it is my only experience with Planar’s so I cannot compare it to others. Extremely airy and dynamic to my ear the have great bass too. The only thing that stopped me keeping them was the comfort. They’re either going to be a good fit for you or they aren’t and it was very difficult for me to get any comfort, try as I might. It was a shame as they sounded great. Also I used the Cipher cable which made a huge difference to the sound over the standard cable.
Just a few of my own thoughts on a couple of iem’s ive come across.