I also ordered two of these, which I use in addition to my existing tie rack, and am very happy with them. They bring some order to my life and I can see all of my ties at one time. I think doubling up would make things pretty tight if it's even possible. You can add some extras but how many depends on the thickness of your ties.
Here's my tie collection now, I'm quite happy with these. I can visualize my entire collection at once and have room for expansion. The top rack was my existing one.
by mjoseph990, on Flickr