Here is a list of commands I have for controlling Pioneer players via the
RS-232C jack.  Hope it helps.  I have also heard that there is supposedly a MCI
driver for Windows but I haven't personally  seen it.  I tried these codes
on a Pioneer machine I have at work using the Windows terminal program and
was able to control the player.  This file is from a public domain file for
the amiga.  I think I also have a C program (also for the amiga) somewhere
if you need it.

Cheers, 
Jim Jackson

** communication protocol:                                               **
** pioneer: Computer activates CTS (pin5) of rs-232 port,                **
** (amiga 7-line handshake)                                              **
** then sends a command sequence and expects 'R' and carriage return(CR) **
** back. ASCII digits used for addresses,etc. Returns frame# as ASCII    **
** digits. Player is string oriented and reverse-polish (arg then verb). **
**                                                                       **

COMMANDS        CHARS    HEX     DECIMAL              COMMENT
----------------------------------------------------------------------------

Door Open       OP                                  open the door
Reject          RJ                                  stop disc rotation
Start           SA                                  start disc rotation
Play            PL                                  (address)PL
Pause           PA
Still           ST                                  still frame
Step Forward    SF
Step Reverse    SR
Scan Forward    NF
Scan Reverse    NR
MultiSpeed FWD  MF                                  (address)MF
MultiSpeed REV  MR                                  (address)MR
Speed           SP                                  integer SP
Search          SE                                  address SE
Stop Marker     SM                                  address SM
Frame           FR                                  set frame mode
Time            TM                                  set time code mode
Chapter         CH                                  set chapter mode
Audio Control   AD                                  integer AD 
0=off,1=Ch1,2=Ch2,3=stereo
Video Control   VD                                  integer VD  0=off,1=on
Display Control DS                                  integer DS  0=off,1=on
Clear           CL                                  clear entry or mode
Frame #         ?F                                  get frame number
Time code #     ?T                                  get time code number
Chapter #       ?C                                  get chapter number
Player active?  ?P                                  P00=door
open,P01=park,P05=still
Disc status     ?D                                  5 bytes and CR returned
(and a few others....)

SERIAL PORT CONNECTION:
 computer   player
 --------   ------
  TxD 2      3 RxD
  RxD 3      2 TxD
  CTS 5      4 DTR
  GND 7      1 GND
------------------

For more info on your type of Pioneer player:

    Pioneer Communications of America, Inc.
    Engineering and Technical Support Dept.
    Sherbrooke Office Center
    600 East Crescent Avenue
    Upper Saddle River, NJ 07458-1827