Well, I operate two E3646A with this driver.
There was an error in it, returning just the measurement from the last activated channel. But this was fixed some months ago. You may search NIs support pages for 'E3646', 'channel', 'IVI', 'measurement' and maybe my nick (LuI). This will probably guide you to my inquiry and the fix.
HTH and
Greetings from Germany!