Don't use Y adaptors.
Run the left and right pre amp outs from the newcastle to the tape in or aux in on the Grant. Try setting the Grant to 1/2 volume then experiment where the volume really should be to be balanced with the L/R and rears. You can either use the internal controls on the Newcastle or just remember where the Grant volume matched the newcastle.
This way, for serious listening, you can just use the Grant/Acurus/CD/ set-up. When using theater, everything will be on but ideally you will only use the newcastle volume, leaving the grant volume set at a pre-determined level.
Run the left and right pre amp outs from the newcastle to the tape in or aux in on the Grant. Try setting the Grant to 1/2 volume then experiment where the volume really should be to be balanced with the L/R and rears. You can either use the internal controls on the Newcastle or just remember where the Grant volume matched the newcastle.
This way, for serious listening, you can just use the Grant/Acurus/CD/ set-up. When using theater, everything will be on but ideally you will only use the newcastle volume, leaving the grant volume set at a pre-determined level.