You are misunderstanding what VISA is. VISA is an API for communicating to GPIB, serial, Ethernet, USB, VXI instruments. What it permits is to write a single driver for a specific instrument and use the same driver for that instrument with whatever bus it uses. So, for instrument A from vendor X, you have a single driver whether you have a GPIB, serial, USB, etc. version. For instrument B from vendor Y, you would have a completely different driver and they would not intercahnge unless they used exactly the same command sets (a very remote possibility). VISA also allows you to swap GPIB boards from different vendors as long as they both have VISA drivers.
There is also a higher level API called IVI (Interchangeable Virtual Instruments). Certain classes of instruments (power supplies, DMM's, scopes, and a few more) have been defined with common instrument functions for each class declared. An IVI class driver (i.e. IVIDMM) can be used instead of a specific instrument named driver and you can then interchange instruments from one vendor to another without changing your program.
Now, for the bad news. Your 6289 does not use VISA and does not fall into any IVI class. I'm not sure about the Yokagawa but I assume that it is the same. The only driver for the 6289 is DAQmx. This is the new data acquisition card driver from NI. The Yokagawa would have to have it's own driver from Yokagawa and you would have to have completely different functions to operate that.
