Hi, mts, PE, thanks for the suggestions.
I'm using Phototherm that has an built-in program for E6. There's a wash step after the first developer, but it uses water. I'm not sure it it is at all possible to introduce a separate stop bath.
As for the development time, I follow the instructions of the C6R faithfully. If anyone is interested, a copy of the instruction is here.
Do any of you think that starter solutions might help? In one of the Kodak documentation for E6 troubleshooting, the lack of starter solution is listed as one of the possible causes, and that's pretty much the last option that I have yet to try.