[Sittler27]

Thanks for the feedback.

My MAudio card has a L/R input as two separate RCA jacks, and a L/R output as two separate RCA jacks.
I have been connecting using only the Right rca input jack to the SPL meter's output (sound card's Right input) and then the Right rca output jack to the receiver.

Are you saying I should use a Y cord to take connect to the SPL meter's output and run the other end to both the L/R RCA input jacks on the sound card?
And then run the L/R RCA output jacks on the sound card to the L/R CD input on the receiver?
And then do the disconnecting as per measurements as you mention?

And lastly, should I use the subwoofer signal for the speaker calibrations as well?