This was a good tip! I played around with2 single delays (pre-stack) comparing with RE-20 pedal having the delay sound I'm aiming for (I have also El Cap which is having same effect but with different EQ tweakability compared to RE-20). And indeed, one can get the quite close approximation with this method. Perhaps the biggest issue here is that using two single delays as virtual single playback heads the second delay is also acting as extra recorder head and gives a different flavour especially with shorter feedback levels. I.e. with two playback head real echo units having feedback at zero you will hear original+2 repeats, but in this approach you will hear 3 repeats. Another thing is that this arrangement takes two effect slots.
After messing with 2 single delays in series and reading the manual (yes, recommended alwaysI discovered the parameter that I was after all the time, 'Cross Feedback' control. Like said in the manual: "Increasing the value beyond zero causes each delay to not only feed its output signal back to its own input, but also to the other participating delay lines. This creates a more diffuse delay rhythm pattern, adding a reverb -like character to the delay."
I tried this already earlier, but the thing I missed was the relation to regular feedback (Cross Feedback will automatically reduce the regular feedback).
So, after fine tuning each and every parameter of the Dual Delay one can get really close to atleast RE-20 that I A/B against. Only thing left different is the builtin preamp/EQ in RE-20 which enables active EQ tweaks and gives some color also to overall sound. But no doubt one can get close with KPA's fine EQ fx blocks. Will give it a try next having the delay part solved.
sound clips please 
