Yeah. Like Nomake said, you don't have the "92 problem" and you don't need the comparator. I reckon the issue you see is due to the serial input buffer overflowing in between being polled by the VWRX software. Presumably the portmon software is changing the port buffer settings in some way that helps. That's good to know.
You could also try messing with the registry values in HKLM\SYSTEM\CurrentControlSet\Services\Serial
technet reference page
__________________
Subaru ECU and TCU Website
1992 Alcyone SVX Version L
1992 Alcyone SVX Version L
1994 Alcyone SVX S40-II
2004 Subaru Legacy 2.5 SE Sports Tourer
1996 Subaru Legacy 2.2 GX Wagon
1988 Subaru Justy J12 SL-II