MIDISynth tool programming questions

[wrh@PHYSICS.WM.EDU (William Hall)]

In using the MIDISynth tool, I have come across several problems/questions:
(I have programmer's ref. for 6.0 and MIDISynth ERS from APDA a while ago)

1. In order to use a MIDI driver, it must be loaded into memory (by me).  By
  looking through the synthLab code, I found that this must be done by a 
  system loader call.  Where can I find the documentation for the system
  loader?  (Possibly GS/OS Ref?)
2. In synthLab, there are volume settings for each individual instrument, set
  by sliders in the volume setup screen.  What do these settings change?
  (i.e., what call can I make in my program to set these levels?)
3. According to the SetTempo call, the tempo range is 10-265 BPM with the
  parameter to the call ranging from 0 to 255 (BPM-10).  So how come synthLAB
  takes the tempo value stored in a song file, subtracts 5, and then multiplies
  the result by 2?
4. How exactly do I check whether AppleTalk is enabled before I start the
  MIDISynth tool?  The MIDISynth ERS and Programmer's Ref. for System 6.0 both
  mention that my program must check to make sure AppleTalk is not enabled.

Thanks to any and all who reply!
-- 
William R. Hall  |  wrh@physics.physics.wm.edu |  College of William and Mary
                 |  hall@wmheg.physics.wm.edu  |  Department of Physics
                                               |  Williamsburg, VA  23187-8795