Channel Change

The old Sansui Amps had a channel change function built into the unit. IOW the L & R stereo functions could be changed.

Since my prev Sony & current Denon do not have this feature, I was compelled to hook up a component between my DAT & Amp that I got from R Shack yrs ago. This small rectangular unit has L & R(RCA)inputs & outputs that enable the same function that was built into the Sansui.

As my unit now need to be replaced & RS apparently does not have it anymore, I am hoping someone knows where to obtain a similar product.
Just curious why is it so necessary? I can't think of a really good reason to switch, which you could do if really needed to just by swtching the interconnects. That is probably why current pre-amps don't have it.
My fav thing is early Beatles. Until IWTHYH, the records were all in 2 track and I had alot of fun with the old Sansui because I prefer to hear the vocals out of the left side.