Hello,
I downloaded the latest Lecroy 930X_1X driver from www.ni.com/idnet and took a look at it. It seems that the driver does support reading from Trace A, and that it sends a "TA:" instead of "C1:" when reading Trace A rather than Channel 1. Since I do not have this instrument, it's difficult for me to determine whether or not this will work with the instrument. Some resources you might consult include Lecroy support, the programming manual for the device to see if there is anything particular that needs to be done when reading from Trace A rather than Channel 1, and also possibly reposting your question with all the relevant details in the Instrument Communication forum to see if anyone in there has that same instrument.
Hope this helps.
Scott