OK here are the good news. I returned back the sampler to the seller, which definitely doesn't know how to use it, so he can't be sure that the sampler worked before I bought it.
Now I have just bought another TX16W, without any memory extension this time. But it works completely. No crunch on the outputs. I can sample from my Shure microphone and from a line input. Testing with my voice reminds me all the tunes of the 80's.
I need now to learn how to use it, which is better between sampling drum loops made with Ableton Live vs performing sampled drum sounds, etc... The game begins now.