This has been bugging me enough to dig out a VDIP1 and take it along with me.

Here is what I got working. First off the "flash stick" was loaded with a file named VOLUME.TXT with 10:255 written in it so I think we are using the same file.

I do not have a VDIP Music module so this is working with a standard VDIP1. The attachment shows the firmware setting.
Name: VDIP_FIRM.png Views: 736 Size: 34.6 KB
Below is my complete code. The long pauses are just there to make sure the VDIP is initialized before sending any commands to it.
The LCD displays 10 for VAR VOL and 255 for VAR VOL2.
I hope this helps.
Code:
'  18F6680  VDIP
' 1384 BYTES
    DEFINE OSC 20
    @ __CONFIG    _CONFIG1H, _OSC_HS_1H
    @ __CONFIG    _CONFIG2H, _WDT_OFF_2H & _WDTPS_128_2H
    @ __CONFIG    _CONFIG4L, _LVP_OFF_4L
    DEFINE LCD_DREG     PORTG
    define LCD_DBIT     0
    DEFINE LCD_RSREG    PORTE
    DEFINE LCD_RSBIT    0
    DEFINE LCD_EREG     PORTE
    DEFINE LCD_EBIT     1
    DEFINE LCD_BITS     4
    DEFINE LCD_LINES    4                         
    DEFINE LCD_COMMANDUS    3000
    DEFINE LCD_DATAUS   150
    
    RXD     VAR PORTE.2    'VDIP PIN 6 - DATA FROM VDIP
    TXD     VAR PORTE.3    'VDIP PIN 8 - DATA TO VDIP
    FLOW    VAR PORTE.4    'VDIP PIN 9 - VDIP RTS
    VOL     VAR BYTE
    VOL2    VAR BYTE
    
    PAUSE 5000
    PAUSE 5000   'SAFE START UP TIME FOR VDIP
    LCDOUT $FE,1,"MACKRCKIT"
    lcdout $FE,$D0," U.S.A."

    'INTIALIZE VDIP STICK
    HIGH TXD
    PAUSE 5
    SEROUT2 TXD,84,["ECS",13] 
    HIGH TXD
    PAUSEUS 10
    SEROUT2 TXD,84,["IPA",13]
    HIGH TXD
    PAUSEUS 10
    WAIT11:IF FLOW = 1 THEN WAIT11
    
    START:PAUSE 5000
    serout2 TXD, 84, ["OPR VOLUME.TXT", 13] 'open file
    WAIT01:IF FLOW = 1 THEN WAIT01
    serout2 TXD, 84, ["RD VOLUME.TXT", 13]  'read file
    SERIN2 RXD, 84, [DEC VOL,DEC VOL2]    
    WAIT13:IF FLOW = 1 THEN WAIT13
    serout2 TXD, 84, ["CLF VOLUME.TXT", 13]  'close file
    GOSUB DISPLAY
    GOTO START
    
    DISPLAY:
    LCDOUT $FE,1,"VOL ",DEC VOL
    lcdout $FE,$C0,"VOL2 ",DEC VOL2
    lcdout $FE,$D0," U.S.A." 
    PAUSE 250
    RETURN