Hi Bevan,
I apologize for the delay... I've been away at the FSI Expo in Montreal.
I emailed you the following info:
Do not use a splitter with the RCA outputs of the Signature 30. The volume controlled RCA output signal also is fed into the amplifier, so if you join the L and R signals together at the RCA outputs, you are essentially joining them together going into the amplifier board inside of the Signature 30 and you will get mono.
You can split the signal after it passes out of the Berhinger.
If you sub has a separate L and RCA input jack, this will be fine too!
If you have any other questions, please let me know.
Best regards,
Vinnie