The Axe (Ultra) combined with KPA just dissapointed me.A Strymon Mobius gave better results, but in many ways the endresult didnt differ that much from the KPA, The Boss gt 001 I found most complimentary.
There is a thread somewhere here about a new fx only floorboard that Fractal Audio is due to release that could be interesting for you, I reckon its gonna be a lot cheaper than the Axe fx itself,
You didn't get much better results with the Mobius? I have to try. I'm a huge Strymon fan, own most of their pedals, but I have had the Kemper barely for days so I couldn't yet try them together.
However, my first impression (without proper a/b comparison) makes me think that Strymon wins hands down. Nothing wrong with Kemper effects, they're very nice and professional, but much more standard than Strymon's, and that's ok, it's not the KPA focus, right? On the other hand I could probably like the KPA delay better than the digital delay on the Timeline, it sounds more pristine.