Quality IEMs will generally tend to have better frequency reproduction, spectrum balance, dynamics, and sometimes spatial properties and build and fit advantages to cheap IEMs. All are generally advantages regardless of what you are listening to.
Depending on the material 192Kbps MP3s might yield a pretty good result, in other instances the result will be noticeably different from the lossless version. Generally, unless the encoding is pretty bad, one might not immediately realize they are listening to an MP3. You may need direct comparison to the lossless version to pick out the differences and nuances that are caused by MP3 artifacts.
The analogy is having had a middle-of-the-road computer monitor for 5-6 years, 1680x1050 resolution, slightly washed out colors and dynamic range. Then getting a brand-new IPS 1920x1080 HD Panel.
Everything will look different, color calibration will change, skintones might improve and seem more realistic, You can better tell subtle brightness differences in the highlights.
However some JPEG-compressed images you have will still look pretty darn good, since they may be more easily compressed due to the nature of their composition. In this case the HD upgrade did yield a different presentation, but doesn't necessarily give you a tonne of new information.
While some other pictures with smooth gradients and subtle tones and hues will immediately betray their compression method by showing banding, aliasing and slight blockiness or smudginess. In this case your eyes will notice that patchy blue sky and you will ever so slightly cringe at how ****ty it looks. Then proceed to do a reverse google image search to find a version of it in .png format.
There will also be that rare instance where you find the full-quality version of something and you may notice annoying small details that weren't in the compressed version, like that slight ringing in the highest frequencies coming from a poor recording or some audio effect that is behaving badly and really shouldn't have been used at all if the sound recordist or mix engineer knew what they were doing. Sometimes the compressed version might actually be preferred over the lossless parent, despite being technically inferior, due to masking subjectively unwanted properties. Cinematographers for films and TV will often use diffusion filters in front of or behind the lens to intentionally soften the image, giving it a substantially less sharp and vivid look. In the long run though this can help with giving a relaxed presentation and not barraging your eyes with constant sharpness (take it too far though and it will make you feel like you want to start squinting in order to try and focus your eyes to see sharper, in which case it is taken too far in the other direction).