Based on schematics I’ve seen for other ARC designs I suspect that the signal pin of the RCA input connector for each channel of the DS450 is wired directly to one of the two signal pins on the corresponding XLR connector, very probably pin 2. And when the RCA input is being used the switch on the rear panel simply grounds the other input signal pin (pin 3) of the XLR connector, while the switch most likely does nothing when it is set to the XLR position.
Given that, at the very least sonics are likely to be adversely affected if both inputs are connected at the same time, and damage to one of the preamps is also a possibility, eventually if not sooner.
As further confirmation, I see on page 2 (pdf page 5) of the manual for the amp statements saying "disconnect any balanced cables" for single-ended operation, and vice versa.
Regards,
-- Al
Given that, at the very least sonics are likely to be adversely affected if both inputs are connected at the same time, and damage to one of the preamps is also a possibility, eventually if not sooner.
As further confirmation, I see on page 2 (pdf page 5) of the manual for the amp statements saying "disconnect any balanced cables" for single-ended operation, and vice versa.
Regards,
-- Al