Mhedbi,Because FSX doesn't handle asymetric thrust well. Taxiing with one engine is pretty hard in the sim.

I don't think that it is impossible. I usually taxi the F1 ATR 72-5 with engine 2 running as it is usually done in reality. The only problem is beginning taxi with a right turn...

With condition levers in taxi, what is the minumum torque you see?

When condition levers are in taxi, the minimum torque I see is somewhere around 7, but when I advence the power levers, after something like 13 it suddenly jumps to 21. Is it the same for you or is there a problem with my throttle settings? I use CH Yoke with levers on it.

I think in regards to the torque jumping it is not your throttle. When you are on the ground you are allowed to pull the props back into beta which decreases the RPM as indicated by the CAP. The reason I think it jumps up to 22% torque is because of what RSR was saying about how it does that to stop the negative torque effect on the props. If I play around with it and move my throttle very slowly I can sometimes get under 22%, I've seen as low as 17%. I usually have no problems taxiing with the torque at 22% though. I just learned what RSR said the day I bought it. Just advance the levers for a few seconds and then put it back in beta for a few, etc. She is a handful to taxi, but certaintly a replication of the taxiing method on the real bird.