Hi Thor, Sorry for the delay, it reached the end of the day yesterday and I felt shattered so I'm afraid I left this until today (especially as I'm a bit rusty on VL stuff).
As far as I recall when using the MU128 and later the MU1000, these things seem to be necessary.
The port and channel on which the VL100 or 150 will respond need to be set up and these are accomplished with SysEx commands. The calling up of the voices in the correct way is also essential and these are done with unique MSB and LSB Bank Select messages.
So here is a screen shot I just put together, displayed within XGworks, that show the 'normal' setup for a PLG-VL card.
1st SysEx: So, apart from the usual GM and XG system on message, we seem to need to assign e.g. Part 1 to VL-XG. (It could be anather part I believe.)
2nd SysEx: Then we need to assign the port/channel (in this case A1) as the receive channel for the chosen part.
It's only then that we can send the appropriate Bank Select MSB and LSB.
The MSB needs to be either 97 or (I believe) 81 works too. But 33 for some (see below).
The LSB needs to be 112 to 119 or one of four others. Again see below.
Note too the careful spacing of XG on after the GM reset, and the spacing apart of SysEx messages.
Send them lumped together and you can get an overload in an MU.
Hope it works. It's been a long time since I used the VL so I'm very rusty with the commands.
I seem to recall reading that it can take an MU unit 100ms or more to actually change all instrument channels back to their defaults, and something like 50ms to do the same with the XG reset. So it's certainly worth spacing these two well apart before entering any other SysEx messages.
I always space these messages five to ten ticks apart at 480tpqn and set the first measure to be 120bpm then start the song at measure two. I often change first measure's time signature to 1/4 or 2/4 (depending how much setup is needed) to get it over with quickly.
As I recall, I wrote a section about timing in one of the tutorials. JohnG.