Just to say that I have had the new par2.exe all the time, and I know it is supposed to utilize all cores...
My problem is only with decoding of huge files. It seems that since alt.binz is stuck at decoding, the repair and unrar can not start.
I tried NewsLeecher on one of the NZB files, and I had no problem at all getting the 7GB. I retried with alt.binz, and it stopped on decoding about 40% in to the download. All files got downloaded, I just had to manually unrar.
So I do think the problem is in alt.binz
I will continue to use Alt.Binz, but hope you sort it out.