Hello everybody,
I am a fresh Kemper user, just received my powerrack unit a couple of weeks ago (to basically replace Peavey 6505 head + POD HD500 floorboard in the four cable configuration). I also have the FCB1010+Uno4Kemper.
At the rehearsal space, I connect the Kemper's speaker output to Mesa Oversize 4x12 Rectifier standard cabinet. Some profiles sound absolutely great with the MonitorCabOff feature whereas about 30-40% of the profiles (of the ones I happen to have in the unit) have a strange "metallic ringing" or piercing high end in them. I try to provide some clips later, haven't found too much information about this problem yet. A similar example can be heard here, although in my cases (=powerrack through cab) it is much more audible (especially with some Blackstar profiles?): http://www.youtube.com/watch?v=QB52leyv6_I
In my home "studio" (aka laptop+audio interface+headphones :D), I use the unit via spdif (reamping etc) and everything works just fine. The effects satisfy my needs totally as well. Test clip: https://dl.dropboxusercontent.com/u/55653919/515…l-test-clip.mp3
Yesterday I created my first profile in a friend's studio, and the profile was 100% there out of the box (Cornford head + OD pedal + Marshall 4x12). We couldn't separate the profile from the real thing, even though the owner of the rig has been using it for many many years and has golden ears 
We also ran the profile through the same cabinet+mic combination by using the built-in poweramp. Here, we noticed slight EQ-type coloration; the dynamics and feel seemed to be unaffected, and the profile responded amazingly well to adjustments within the unit.
We also tried to grasp the "amp in the room" aspect of the profile by comparing the real rig and the profile+built-in poweramp+cabinet (wíthout miking the cab, that is), and these were very very close to each other as well.
For my narrowish death metal needs, the PowerRack really delivers it all, and the built-in poweramp is a nice extra thing to have if you like to have a real cab around. The built-in poweramp works much better than I expected based on certain reviews/opinions expressed on the web, this is something I want to emphasize!
This forum has been very useful so far so thank you guys and thank you Kemper! 
