If you want to try the link with two cars out on a single machine:
Get the link-cabmame binary linked here, extract, and put it in your MAME folder:
http://www.mameworld.info/ubbthreads/showthreaded.php?Cat=&Number=303661Create a
vr2.bat batch file with:
start /b cabmame.exe vr -w -nvram_directory nvram1 -localport 15111 -remoteport 15112 -localhost 0.0.0.0 -remotehost 127.0.0.1
start /b cabmame.exe vr -w -nvram_directory nvram2 -localport 15112 -remoteport 15111 -localhost 0.0.0.0 -remotehost 127.0.0.1
This launches two instances of MAME with separate non-volatile memory [nvram] folders.
Having separate nvram folders allows each instance of MAME to be defined as specific car.
In one window configure Car 1 as RED/MASTER, and in the other window configure Car 2 as BLUE/SLAVE or LIVE Commentary.
Press F2 to enter TEST MODE:

Configure Car 1 as RED/MASTER:

Configure Car 2 as BLUE/SLAVE for
Car 1 vs Car 2:
-OR- Configure Car 2 as Any Color/LIVE for the Virtual Race Commentary.

EXIT and SAVE THE CHANGE:

Quit MAME and restart the vr2.bat file.
The two windows should now link.