Ralph, firstly, be careful of using generic terms to describe something. When we talk about asynchronous communications it normally refers to the stuff we send down RS232, however, when we talk about synchronous communications then that opens up a pandora's box of possibilities. Simple saying 'synchronous' tells us very little apart from the transfer is related to a clock signal. For example:- i2c is synchronous as it USB, but you'll find these two synchronous protocols are vastly different.

At last you've mentioned the memory card for PS2 which gives us much more of a clue as to what you want to achieve. A quick search of the web turned up this site:

http://www.zen35383.zen.co.uk/stnield/psxpads.txt


Usually, synchronous comms are done at a much higher speed than async comms, so that makes the whole thing a lot different. Due to the higher speed, the databoy hardware is probably not suitable without major modification. Sure you can do it in discrete logic, you could do it using transistors if you like, but nowadays we have fpgas and cplds that make the job easier.
Why do it with a databoy? - I think you'd be making the job harder for yourself. My first stop would be to use a logic analyser. You can get some nifty small ones that hook into the USB port of your PC. Some even have scripting so you can have it decode the commands etc to make the data readable to humans.

I'm not sure of what your goal is with your suggestion: is it to make the databoy read PS2 memory cards? Where does Linux fit into the picture? How would it talk to the memory cards differently than the PS2 code?