ник: ShadowOfSun
На первый вопрос держи ссылочку
http://www.sql.ru/forum/actualthread.aspx?bid=22&tid=248037&hl=%e3%f0%ee%ec%ea%ee%f1%f2%fc 
громкость микшера 
либо так
Option Compare Database
Option Explicit
Private Declare Function waveOutSetVolume Lib "winmm.dll" (ByVal uDeviceID As Long, ByVal dwVolume As Long) As Long
Private Type ulLong
HiWord As Integer
LoWord As Integer
End Type
Private Type uvLong
n As Long
End Type
Private ulVol As ulLong
Private uvVol As uvLong
Public Function SetVolume(Volume As Long)
' Максимальное значение параметра Volume = &HFFFF&.
ulVol.HiWord = (Volume And &H7FFF&) - (Volume And &H8000&)
ulVol.LoWord = (Volume And &H7FFF&) - (Volume And &H8000&)
LSet uvVol = ulVol
Call waveOutSetVolume(0, uvVol.n)
End Function
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на третий вопрос тоже ссылка
http://www.sql.ru/forum/actualthread.aspx?tid=693609