Sorry to hear of your dissatisfaction. Just for the record the I was disappointed with the KPA initially too, I now see it as the best gear purchase ever.
The Kemper is a professional tool, it’s deep and as a plug and play device you will be disappointed.
Buggy connection with rig manager is not normal, I would seek support.
A proper editor is a probably the the #1 issue for a lot of people, there is a third party option available but I have not personally used it, maybe someone else here will chime in.
Fizzy hi gain tones?, well the KPA profiles the whole signal chain, amp -cabinet -mic.
It is most probable the the cab or mic are not pleasant to your ears. I suggest you adjust the cabinet parameters to your liking or swap the cabinet completely. I almost always reduce the high shift on the cab settings, just a touch a little goes a long way here. Just like the real world it’s all about the cab!
Navigating the KPA is breeze, just got to learn how to use your tools, there may be better out there these days but there is plenty of dedicated knobs and buttons to assist you. The exception here is effects preset management which is my personal #1 issue but it is promised to be addressed by the KPA team in the next update.
The remote was designed primarily for live performance and as such The KPA team wanted to avoid the tap dance for effects switching and introduced a different paradigm. Instead of the 1 footswitch = 1 effect you can add multiple on/off commands to multiple effects. For example with the tap of one switch you could add a boost, turn off a compressor and swap out a long delay to a slap back. It’s incredibly easy to apply this, just hold the foot switch and press the corresponding effect button and they are connected, do the same with the next.
USB cable, well ok.
Tones not cutting it?, you have an absolute wealth of profiles at your disposal, I assure you there is no other machine that can cop the tone and real amp tactile feedback of an amp like the Kemper, it just takes some searching, time and a little no how to personalise it to your taste and ears.
Bottom line the Kemper is not a plug and play solution but will reward in spades in time, read the manual, watch the how to videos on there site, a good place to start.
Peace.