Just to make it clear, a USB->Serial converter is simply as said - it converts USB to serial. Just because they are often sold as a 'flying lead' it doesn't mean that they wont need a serial cable or adaptor in their own right. A number of time recently on a number of BB's I have seen people having problems with USB/Serial converters simply because they did not realise that they needed additional equipment in the chain. Often require a null model adaptor or cable is required - as is necessary with Meridian kit.

The null modem adaptor/cable has the tx and rx lines crosslinked - this allows DTE (Data Terminal Equipment such as PC) to DTE connection ie PC to PC rather than DTE to DCE (Data Communications Equipment such as a modem) ie PC to modem. Whether a piece of kit acts as DTE or DCE is down to how the connection is viewed by the manufacturer, but as a general rule, something that terminates a communication chain (ie PC, Meridian processor, maybe your projector) is a DTE and something that is part of a comms chain (ie modem) is a DCE. If you are trying to perform DTE to DTE comms, you will will require some form of null modem adaptor, be it a cable or adaptor box/dongle. A null modem adaptor is more than a 'gender bender'.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).