Tube buffer in tape loop@

Hi,I recently bought an Esoteric K03XD, which sounds absolutely amazing with most albums. I find some 90’s rock sounds a bit harsh, and I was considering adding a valve device. I use a Bryston MP26 pre-amp, and I was wondering if inserting a valve buffer (Icon Audio BA3) in the tape loop might be an idea.

Icon Audio suggests that the buffer is best placed between two components. As I really like the sound as it is for most albums, I am reluctant to do this. I was hoping that placing it in the tape loop might enable me to listen to the CD player, or any source, and hear the source as per normal when the switch on the Bryston in the "source" position, and hear the processed sound with that switch in the "tape" position.

Is that correct?
I came across a rather alarming post in a forum saying that this works, but that it is possible to seriously damage components or speakers if you put the switch in the "source" position. That seems odd to me, but there is so much I know I don’t know that I tend to be a bit cautious. Any advice would be appreciated.
Thanks.