The old AK120 is more "analog" sounding, less detail, more smooth/richness to the sound, and it runs on a more primitive UI. The AK100ii has a more clean and neutral sound signature with greater dynamics and detail retrieval, and boasts a more advanced UI. I had the same decision to make a while back and I chose to go with the AK100ii, simply because the UI was a lot less cluttered and refined, and the ease of use was improved vastly. In terms of sound alone both are different but one isn't necessarily better than the other, just different tonality for different tastes.
If you're going to be using it with your JVC IEM, which is rather warm sounding the cleaner AK100ii may be a better bet for you, IMHO. Hope this helps!
EDIT: Just to clarify, both models have WiFi streaming and Bluetooth, it's only the AK100 that has the wireless updating.