Curt, I think you are out of luck with the ST_E2 & non-Canon flash(s) for full E-TTL. As the CANON system uses IR instead of radio waves or optical sensors, it will only work with Canon strobes that can process IR. You can still use the YN strobes in ETTL by using a CANON synch cord / cable or a much cheaper China synch cord (knockoff). I use the China made cord and hacked it so I can clip a short 1 metre, 3 metre or 10 metre long LAN cable into the synch cable and thus able to use full ETTL OFF camera with my Canon strobe(s) or ETTL compatible non-Canon(s).......... Don't know of any non Canon strobes that operate on the IR system used by Canon. AFAIK..... I also use the Poverty W's plus just started using the YN RF 602 set(s). Work great for hobby use as I'm now retired. Still use the Povertys for kicker/hair/side strobes as needed.
Curt H.
"el Condor loco" GRAPHIX
Queensland, Australia
"el Condor loco" GRAPHIX
Townsville, Queensland
Australia