Finally I could use the download master! The last firmware version+ Asus utility is working properly for nearly two weeks.
I was able to download more than 30 G of usefull stuff since then.
The only remark I have is that the external drive (a Kingston 32 G G2 flash drive) has to be formatted in EXT2 (Ext3 would not work).
The PC interface is still buggy and sometimes I have to load the information several times untill I get a message "file already exists" just to make sure that the info has actually been transferred to the router.
Also, it REALLY takes time to transfer files to the external drive to the PC.
typically a 700 Mb .avi file would take about 5 minutes to be copied to the PC HD.
However, I am not sure if this low transfer velocity is caused by the firewall/anti virus installed in the PC.
Any suggestions?