Is it safe

One further thought, adding to my previous post: Noise that may enter the amp via the RCA cable while the XLR input is being listened to will not be rejected by the amp's balanced input circuit, since it will be present on only one of the two signals in the balanced signal pair. That might impact sonics. The amount of noise that is introduced into the RCA input in that situation may be much greater than when the RCA input is being listened to, since the powered down RCA source will presumably have a much higher output impedance than when it is powered up.

Regards,
-- Al

Don't do it unless the vendor's tech expert assures it is OK.

Al's post is nothing if not succinct, detailed, and absolutely reasonable...you know...now that I think about it, maybe my sister is bipolar.

Thank you everyone and Thank You Almarg for your well explained response. Once again I am amazed by the depth of knowledge and willingness of the members of this site to help each other out.It looks like with the potential to do harm, even in the long term to my equipment I am just going to bite the bullet and get a preamp.