Hello, you can get there by driving thru Tusen Mun and through the beach area, it is almost at the most western tip where the road ends.
Unfortunately, it is expensive and the course is not very good. For example, when you first started, they will give you a beginner type 4 stroke engine go kart which is not very fast. Then if you want to get the 2 strokes fast go karts, then it is major big bucks. 1500 for a day or 300 for 10 minutes.
Fortunately, there is one being opened in Shenzhen. It is actually more convenient to get to from HK, cheaper, and the cars are faster. It is 15 minutes cab ride from the border crossing, and it should open within the next month or two. I can keep you posted.
The Tsuen Mun one is ok if you do not mind the drive out (full 45 minutes on the highway) and want something of a quick fix, but it is definitely not something that you can go to on an ongoing basis.