RS232C between SRX611 and PC

I have no idea what an SRX611 is, just some serial comm experience. The manual I found for SRX611 talks about LUNA software V5.0 the requires DOS 5.0 or higher.

Windows changed serial communications dramatically between DOS/Win3/95/98 and Windows NT/2000/XP and higher. As I recall the Windows 3 (for SRX diagnostics) used DOS for driving the COM port.

There could be significant issue addressing the COM port at all if you're trying to use any current version Windows with that old software.

The word Baud does not appear in the manual, so it was probably a fixed, default setting in the device, spec'd in some other manual.

The 2 to 3 and 3 to 2 wiring is conventional transmit-to-receive and receive-to-transmit, which does not provide for hardware handshake. If there is handshaking, then it would have to be software handshake.