I suggest you check the north taiwan offroad facebook page. facebook.com/taiwanoffroad I think.
Look at an ariel map of Taoyuan, you will see the eastern boundary is a mountain. Riding all over that hill is possible, but from what I gather the DH track area has been consigned to history. I went there last week and it hasn't had much use recently. I was told of the landowner threatening someone with a hammer a couple of months back (!) but I can't vouch for that.
There is said to be a new location over the hill near Linkou, but I looked on the ariel map and it looks very small with little elevation. Might be OK for jumps, but no DH racing possibilities.