mp3 compression really fucks up the high frequencies, far worse than the low ones one could say, the higher you go in frequency the more easy tiny detail gets messed up so yea i guess ambient with lots of long subtle sounds, complex textures and high sounding pads get fucked up faster. if a background noise consists of complex textures all of this depth easily gets lost (aka fuzzy, in playback) in mp3 conversion since quality is sacrificed for file size saving.
also mastering isn't as powerful in ambient music as in psytrance i would dare to say, so the waveforms themselves aren't as tuned up as psytrance music which means they perform less on a lower volume level compared to hard mastered psytrance.
from what you put i'd just say a bad rip and/or conversion. 192 CBR is supposed to be doable
mp3 conversion:
basically mp3 compression reconverts your file into a cut spectrum between 20hz and 20khz and uses a customizable (VBR etc) algorithm to create a flattened (and thus smaller in filesize) image of your song, so underlying and higher frequencies get cutoff from the song's dominant frequency area throughout the playback
the main effects are dryer overall spectrum, less performance and great detail loss on higher volume levels and loss of stereo/depth perception as well as simply output demand on your stereo, so now matter how hard you power your amp and tune up your speakers (and raise the volume), that mp3 ain't gonna shine brighter it's the same story in digital photography btw of RAW vs JPG, each time you compress a jpg into another jpg, there is quality loss, if you convert a 192 kbps mp3 into the same thing, there will be quality loss, since the algorithm the compression/conversion is based on only thinks of space saving.