Hi ganq!
These are wikipedia pages for the trees...
http://en.wikipedia.org/wiki/Agathishttp://en.wikipedia.org/wiki/Picea_glauca (Shin-kaya is this one)
The visible difference of these two gobans is the color.
You may notice this by looking at the pictures on ebay

, shin-kaya goban is somewhat goldish, while agathis goban more darker maybe light-brown.
But you can't pay more $500 for color though...
Well, the kaya goban is considered the best for its color, sound when you place stones, durability, fine scent, and many others.
The shin-kaya is considered similar to original kaya, while it is actually a different type of tree. It may be a good choice if you want fine quality from moderate price.
Agathis is the most popular tree in making gobans, for it is so common to find from Indonesian rainforests. My own goban is agathis

, the biggest problem of this I think is the stone placing sound. It is very dull.. not just mine, also the same in the gobans of my local go club, which are also agathis. However, unless you are too sensitive on sounds, I recommend this one, more than shin-kaya. Maybe I think $999 too expensive for a game board

.
BTW, there is a korean goban shop also online,
http://www.hanilbadook.com/goods/produc ... tg_code=01 . I actually told you about here before, and it does support oversea delivery.