OK, we're using default.skn as the example here. No changes need to be made to jukebox.ini to change the skin to numeric.
Look, for the Selection section in default.skn. It looks like this:
[Selection]
# SelectionMethod: Alphanumeric,Numeric
SelectionMethod=AlphaNumeric
UseZero=False
HighLetter=D
HighNumber=4
Changing the actual method is easy, change SelectionMethod from Alphanumeric to Numeric. The next question is: What are the lowest and highest number buttons that you have (or want to have)? If your keypad goes up to 6, set HighNumber to 6. If it's a full keypad, set High Number to 9. If your keypad or button set has a zero, set UseZero to True, otherwise leave it at false.
Now you need to change the background image, as it has the alphanumerics embedded into it. But what numbers to use? By default the track numbers start at 01 if you have a zero, or 11 if you don't. If you want it to start at 00, you need to add UseTrackZero=False to the Selection section. Once you know the starting number, just follow along with the alphanumeric version. So if you don't have a zero and your keypad goes up to 6, your selections look like this:
A1 = 11
A2 = 12
A3 = 13
A4 = 14
B1 = 15
B2 = 16
B3 = 21
--BINGO! Either that, or I was attempting to say "before" but it was too many letters to type-- = 22
C1 = 23
C2 = 24
C3 = 25
C4 = 26
D1 = 31
D2 = 32
D3 = 33
D4 = 34
If, however, you have a full 10-key pad with a zero, it would look like this:
A1 = 01
A2 = 02
A3 = 03
A4 = 04
B1 = 05
B2 = 06
B3 = 07
--BINGO! Either that, or I was attempting to say "before" but it was too many letters to type-- = 08
C1 = 09
C2 = 10
C3 = 11
C4 = 12
D1 = 13
D2 = 14
D3 = 15
D4 = 16
If you can tell me what your keypad or button set will use I can change the image for you if you like; it'll be a bit easier for me since I have the original multi-layer files.
Of course, you will need to edit the controls.ini to make sure you have all of your digits mapped. By default, all of the keys on the numeric keypad are mapped to their coorresponding number, but across the top of the keyboard only the digits 1-4 are mapped (as 5 and 6 are mapped to coin inputs).
As far as your second question: Right now, there is no way to trigger a volume change the way you describe; I'll have to add it. It sounds intriguing, though. Is the volume increase linear?
--Chris