Got it to work. What you have to do is, in the Multi Window, when you select an instrument for each slot, you have to pay attention to the ordering. The top slot is "1" and the next one down is "2" etc... to "8" at the bottom. And when you set the MIDI track, you select the output to be that VST, and where it says Channel: ANY- this has to change to correspond to the correct channel number you want to play that track. For example, if I put tubular bells in the second slot in my Multi, then when I select a channel in the MIDI track, I have to choose channel 2 if I want the bells. As far as I know, you can't assign multiple instruments to a single track (with the exception of "instruments" that already consist of many in 1 slot in the VST).
So 1 instrument per track, 8 loadable at a time (barring multiple instances of the VST), and if you want multiple instruments per track, you have to duplicate the track.