Generally speaking any effect or device that will bring your signal up to "pro" line level (rack effects level) will work in the loop. I successfully used an Alesis Nanoverb to bring the return level up and use my pedal board without a D-later. So if the DBX has enough makeup gain to sit in front of your pedals and bring the signal up then it will work. The Klienulator does a great job of further smoothing of the overdrive sound (as does the C-labor) so you would miss this benefit.

Hope that's helpful