I finally succeeded in purchasing train tickets that were almost exaclty what I wanted!
The guy at the ticket counter spoke English, but it probably would have been more successful had I spoken Chinese with him; his English was pretty bad.
He first had me going to some completely different city...I don't even know where it is. I got it sorted out, and I'm going to visit Kari in Xi'An next weekend!
Yes! It's even a sleeper ticket (not only do I have a seat, but I have a BED!).
Terracota warriors here I come!