I updated to fw2.2.0, so far so good! Haven't come across the problems I experienced on 2.1.8 

For those who curious about how sharp/slow roll-of works... or does not!
Well, you need to have headphones and ears to hear high frequenciesDownload "Mosquito Tone 2 (Modulated)" from here. With 2.2.0, play it and switch between sharp and slow settings while it is playing. Do you hear any difference? If you don't hear a difference, or just hear nothing, then, probably, you should not bother about this setting at all.
Now, if you hear the difference, leave it at slow, and allow to play to the end. Press "Play" button to start it again. Note, that the sound is the same.
Install 2.1.5 (2.1.8 is unable to play this file!), play that file and ensure that you still hear the difference. Then let it stop with slow, and play it again. Note, that now it sounds like with sharp value. That effectively means that before 2.1.8, the setting worked only for the first played track, and now the bug has been fixed. My sorrow to those who thought that slow sounds better for him before FW 2.1.8![]()
Well, but what does cause the difference? The simple is: distortions, parasitic sounds that should be filtered off.
So, if you still wonder what setting is the really best, my answr is: the best is to use hi-res records, because for them the filter works in ultra-sonic area, and the setting does not really matter![]()
Please try another cable if you can.
Can you read your micro SD Card contents on your computer when you insert the card in an SD card adapter/memory card reader?
you can update your firmware by copying the update.img to the root of a FAT32 formatted sd card (via cardreader). After (re)starting the dx90 in recovery mode [Power On][Vol up], the update will be processed by selecting "update firmware from sd card".
how do I format my sd card from exfat to fat32? lol
Sorry for the newbie question
After additional comparison of 2.1.5 L2 and 2.2.0 L0 on two DX90, IMO it is almost too close to call. The 2.1.5 seems to retain a little more energy and sound slightly more dynamic. I've been using the ESW9LTD to compare the two firmwares, which is a very smooth headphone...so the last thing I need is a firmware that adds additional smoothness...for fear of creating "boring" sound.
If you are on Windows google guiformat
2.2.0 sounds more boring than 2.1.8 and even 2.1.5 from memory. Going from 2.1.8 I immediately felt like the bass was missing. The presentation also felt too laid back for my preferences. Even though you get more transparent mids, it felt too analytical to me. Flatter, yes, but by extension somehow more boring to my ears. Didn't help that I forgot how ugly the font was since I used Lurkers' Roboto. Switched back to 2.1.8 L0 after about 30 minutes of listening.