I guess I'm the only one with the SEM4 around here so far.
The SEM1 and SEM3 modules (ESS based) are not necessarily the typical A&K sound. Especially SEM3 has an analytical presentation with great detail, sound stage and resolution. It has been the best module you can attach to the SEM3 in my opinion.
Or is it?
Well, as soon as the SEM4 arrived, it's not easy for me to pick just one. The new module sounds much more like A&K signature, with creamy mids, deep and wide staging, excellent imaging and treble extension with lots of micro details. Overall, the SEM4 makes the SE180 a great cheaper alternative to the SP2000 in my mind. I have used the SP2000 for over a year, so I can say that this setup is not SP2000, but it's not far away either. For SP2000T idk, I haven't got a chance to test it.
I haven't played around much with the "DAR" upsampling setting, but as a very first impression; it opens up the staging a bit with more spaciousness. It sounds immersive and wide. It converts basically everything to DSD, so yeah, very interesting feature.
Of course, the DAP costs around 1900$ with this module so it's up to you to decide if it's worth it. But if you're after a focused, analytical and sharp sound you can pick the SEM3. The SEM4 is for the people who are quite familiar with A&K sound. But boy, it sounds really good.
I'll do a review on HFN but I thought this quick impression would help.