I have been using the log files. I haven't been able to glean much from them. Here are examples of launching a vpx table, mame with -rompath, and mame without -rompath. Both mame entries open mame. The first one successfully opens the game but PinballY doesn't see it. The second one doesn't open the game as the command line would, again, PinballY doesn't see it. In both cases, there is a process in the process list called mamep.exe.
Table launch: Diner, table file Diner VPX 1.2, system Visual Pinball 10
+ launch: full table path C:\Pinball\Visual Pinball\Tables\10\Diner VPX 1.2
+ table launch: table file C:\Pinball\Visual Pinball\Tables\10\Diner VPX 1.2 doesn't exist; try adding extension -> C:\Pinball\Visual Pinball\Tables\10\Diner VPX 1.2.vpx
+ table launch: file + extension (C:\Pinball\Visual Pinball\Tables\10\Diner VPX 1.2.vpx) exists, using it
+ table launch: executable: C:\Pinball\Visual Pinball\VPinballX.exe
+ table launch: applying command line variable substitutions:
+ Original> /minimized /play -"[TABLEPATH]\[TABLEFILE]"
+ Final > /minimized /play -"C:\Pinball\Visual Pinball\Tables\10\Diner VPX 1.2.vpx"
+ table launch: process launch succeeded
+ table launch: Close Game command received
+ table launch: game exited normally
+ table launch finished successfully
Table launch: Donkey Kong, table file dkong, system Mame
+ launch: full table path C:\Roms\dkong
+ table launch: table file C:\Roms\dkong doesn't exist; try adding extension -> C:\Roms\dkong.vpt
+ table launch: file + extension (C:\Roms\dkong.vpt) doesn't exist either; sticking with original name (C:\Roms\dkong)
+ table launch: table file C:\Roms\dkong doesn't exist; try adding extension -> C:\Roms\dkong.vpt
+ table launch: file + extension (C:\Roms\dkong.vpt) doesn't exist either; sticking with original name (C:\Roms\dkong)
+ table launch: executable: C:\Pinball\mameplus\mamep.exe
+ table launch: applying command line variable substitutions:
+ Original> -rompath "[TABLEPATH]\[TABLEFILE]"
+ Final > -rompath "C:\Roms\dkong"
Table launch: Donkey Kong, table file dkong, system Mame
+ launch: full table path C:\Roms\dkong
+ table launch: table file C:\Roms\dkong doesn't exist; try adding extension -> C:\Roms\dkong.vpt
+ table launch: file + extension (C:\Roms\dkong.vpt) doesn't exist either; sticking with original name (C:\Roms\dkong)
+ table launch: table file C:\Roms\dkong doesn't exist; try adding extension -> C:\Roms\dkong.vpt
+ table launch: file + extension (C:\Roms\dkong.vpt) doesn't exist either; sticking with original name (C:\Roms\dkong)
+ table launch: executable: C:\Pinball\mameplus\mamep.exe
+ table launch: applying command line variable substitutions:
+ Original> [TABLEFILE]
+ Final > dkong