I have the 49txi and recently upgraded from a rp91 to a pioneer 50avi. With this upgrade I was finally able to make use the ilink.
First, I love the 59avi, and it has several benefits for me over the rp91. However, I am not convinced there is a big sound difference with multi-channel music using ilink with this player and analog-audio with the rp91.
Not exactly a black and white test, but my impressions.