Which device to use as the pre-amp

What benefit do you hope to achieve with both of these in the signal chain? Seems counterproductive to good sound if you ask me.

The A12 has the convienence of blue tooth for streaming and remote control functions. Also I use mainly at bedtime and can tell it to shut off in 30 minutes through an echo.

Have to agree with Ozzy.

That said, if you want to take advantage of the features of the A12 then use it as the pre. Does the Marantz have preamp inputs?

The Marantz has power amp inputs and the Rotel does not and since you want the remote functions, etc., you really only have one choice. Run from the 'pre-amp' out on the Rotel to the 'main in' on the Marantz.

Why would you want to use an old 26wpc Marantz receiver that probably didn't sound all that great when it was brand new? Just use the Rotel until you can get something better.