Delay pedals that work in a feedback loop

[marmora]

Looking for recommendations for delay pedals that interact well with a KROK feedback looper.
Schematic below

I've tried a number of commercial and DIY (PT2399) pedals that do nothing when the feedback pot on the KROK is turned up. I'm aware everything in the signal path makes a difference. For example, with a filter in front of the KROK, sometimes things are more tame.
Wondering if anyone has any positive experiences they can share. Post your commercial or DIY recommendations. Thanks!

So far I've had the intended effect with a:
Digitech Digidelay
Akai Headrush
Lectric-fx Memento

http://smg.photobucket.com/user/mrnico/media/Feedback20loop.gif.html