I just finished installing my KD-S100. I still have some tweaking to do but here are my initial thoughts.
My speaker setup is just a pair of 3.5s, pair of 6x9s and a JL 10w4 subwoofer.
The sound is decent so far but the highs seem a bit rough and I think I can hear some "digitizing" for lack of a better word. The bass response is kind of "airy" almost like I have a ported box. Again, sorry as I am not very good at describing audio.
The front right speaker sounds way worse than the front left for some reason.
As for things that I can describe easily, a lot of the feature set make me sad.
The USB is limited to 4 gigabytes, which is pretty low these days. I was using a 500 gigabyte passport with my old HU. The SD is even worse, at it only supports FAT16 and that means 512 megabytes!
There is a long loading time for both the USB and SD. This is not even just the first time you plug them in, but every time you turn the unit on.
I hope they come out with some sort of firmware upgrade for this if possible.
It seems to forget where you were sometimes when you shut it off. Also forgets that random was on.
There is no parametric EQ of any sort. You can adjust bass and treble though, and there is a seperate control for subwoofer. I am hoping this can be alleviated by the ability to make custom profiles with the DPS chip.
I like that it has a low pass filter/cutoff for the subwoofer. It would be nice if you could disable it but not necessary as you can just turn it all the way up.
The faceplate is nice as I am not used to having a multi-line display and I am not sure how I lived without it. I am kinda surprised car audio doesn't have better quality screens yet with the cheapness of full color LCDs these days. You can get a full portable dvd player for $40 at walmart and car audio is still striving with monochrome.
All in all the feature set is kinda disappointing for a HU with a MSRP of over $600.
At the going rate of around $100 I would have no problem advising friends to get it as a cheap solution to get better quality sound but I think I am going back to my old setup.