Hi,
I don't have any readme file about my soundset, because I use a soundset included on Sibelius. But I found a readme file downloading the previos version of the soundset, it is here, in Vienna page. Go to User Area / DVD Products / Needfull Things. There you'll find two Soundsets for Sibelius. One for each version: 5.1 or 5.2. If you are using Sibelius 5.2.5, you don't need any of this soundsets, because the version included with Sibelius 5.2.5 is better and correct. But, if you want to read this readme file, you can just download these soundsets for that.
I don't know why you can't hear "portamento" correctly. The solution aported in this post, worked fine for me. If I discover something more, I will explain it here.