Beijing -> Hong Kong

We'd like to do this journey on 26 September this year but I've seen conflicting information about ticket availability for Deluxe Soft Sleepers.
1. What is meant by the statement that the ticket is only available at stations in mainland China? Can it be booked in advance (e.g. through yourselves) and then collected from the station in Beijing on the day?
2. Can the booking be made from 60 days in advance?
3. The chinatravelguide website train booking system doesn't seem to recognise the route. How can I make a reservation?
(b.t.w., I'd have asked these questions directly by email, but I can't find an email address on your website.)