I think the Luxman c900u amp (maybe it was m900u) could do this but the comment above about the cumulative load even if A or B is selected may also apply here. I was reading about this years ago when I also wanted to use 2 sets of speakers with 1 amp.
I decided to get a preamp that had good RCA and XLR outputs and then got 2 amps. Ideally the plan was to get the COD 07x preamp with dual XLR outputs and then get 2 amps. Unfortunately, I found the 07x to noisy and sold it.
Another option is to call Doug Dale at CODA and see if they can do something custom for you. They have done some customization for me in the past to the #8 amp.